In this chapter, we review and discuss the literature on the use of natural health products for promoting sexual function and healthy aging. Our research has been predominantly drawn from peer-reviewed journal articles, books, online databases, and e-books. We begin by illustrating the growing proportion of elderly people throughout the world, examples of sexual dysfunction in aging adults, and aging adults’ use of natural health products. We then expand on the purported uses of two organisms from each of the five kingdoms of life. After discussing the natural health products, we describe traditional usage, current usage in allopathic medicine, potential bioactive compounds, the physiological mechanisms by which these compounds act, and a conclusion about efficacy. Lastly, we discuss implications for future research directions.
aging adults; sexual function; sexual dysfunction; traditional medicine; natural health products; North America
Globally, the number of aging people 60 years and older is expected to more than double from 841 million people in 2013 to more than 2 billion by 2050 (United Nations, 2013). People in North America have among the highest life expectancies in the world (Rodrigues et al., 2012). Approximately 14% of people (one person in every seven) from the United States of America (US) is part of the older population (65 years and older). United States citizens in this age group have increased from 36 million in 2003 to 45 million in 2013 (a 25% increase), and their numbers are projected to more than double to 98 million in 2060 (US Department of Health and Human Services, 2014). In Canada, senior citizens make up the fastest-growing age group. In 2011, an estimated 5 million Canadians were in the age bracket of 65 years and older. That number is expected to double in the next 25 years to reach 10 million by 2036. It is projected that by 2051 about one in four Canadians will be 65 years or older (Employment and Social Development Canada, 2016).
From a global standpoint, the idea of “healthy aging” or “aging well” is a concept embraced by many older adults. Moreover, sexual dysfunction among aging adults is an important public health concern. In men, impotence is a major well-being concern and is associated with aging (Feldman et al., 2000). From 40% to 60% of older women in the US are affected by sexual dysfunction (Ambler et al., 2012). Older adults are inclined to use dietary supplements, also known as natural health products (NHPs), as a remedy for sexual dysfunction. As a class, NHPs include herbal preparations, vitamin and mineral supplements, and traditional and homeopathic medicines (Vohra et al., 2012).
Natural health products have been used in a variety of styles of medicine such as traditional Chinese medicine (TCM) and traditional Indian, or Ayurvedic, medicine. For example, Panax ginseng is an herbal aphrodisiac that has been used by the Chinese to increase libido in men (Chan, 2012). The use of NHPs in different traditional styles of medicine have encouraged scientists to further study their bioactive components (Chan, 2012). Unfortunately, traditional Native American medicine and derived natural health products from North American organisms are underappreciated. Thus, in this brief literature review, we will discuss possible therapeutic value of native North American bioactive organisms for sexual function, with a focus on aging adults.
To provide a sampling of native North American organisms or derived NHPs that may improve the sex lives of aging adults, we have separated this review into the five life kingdoms: Animalia, Plantae, Monera (Bacteria), Fungi, and Protista. We will discuss the topic of sexual dysfunction by introducing two different organisms per kingdom; each organism is discussed briefly in regards to traditional uses and followed by evidence-based studies.
Organisms belonging to the biological kingdom Animalia are eukaryotic and multicellular—that is, their tissues are made of cells and have a nucleus enclosed by a nuclear membrane. The cells have a cell membrane but lack rigid cell walls unlike members of the Plantae, Bacteria, and Fungi kingdoms. Animals are heterotrophs, meaning that they obtain their energy from feeding on other living organisms.
According to Save the Rhino International, someone who possesses a rhinoceros horn in countries such as China and Vietnam is seen as having elevated social status. Apart from the common image of the horn as a status symbol for elites, when powdered, the rhino horn is highly regarded as an ingestible sexual stimulant that can improve a man’s sexual life (Puri, 2010). It is thus no surprise that rhinoceros poaching has become a big problem throughout the nations of southern Africa, driven by a growing demand for horns among Asian countries (Becker, 2012).
Despite a common Vietnamese belief that the rhino’s horn has aphrodisiac properties, no scientific data support these claims (Puri, 2010). This folkloric reputation has contributed greatly to the endangerment of this species (Puri, 2010). Researchers from Save the Rhino International claim that when poachers from China and Vietnam tranquilize rhinos to cut their horns, they leave the animals to bleed to death.
Antler velvet from caribou (Rangifer tarandus), a North American reindeer, has been similarly used as a supplement by men and women to stimulate sexual desire (Caspari and Robbins, 2003). While the antler is still growing, a vascular skin known as velvet covers it (Hall, 2005), supplying nutrients and oxygen to the growing bone (Hall, 2005). Unlike rhinoceros horn, velvet and antlers can regenerate every year (Puri, 2010). Research has been conducted in Canada, New Zealand, Japan, Korea, and China showing that antler velvet from R. tarandus demonstrates androgenic and gonadotrophic effects that may help regulate the physiological processes of sex organs in men and women (Puri, 2010). For example, pantocrin is a natural product that can be extracted from velvet from R. tarandus antlers and consumed by people, purportedly to increase libido.
Not many studies have been done to find strong evidence that antler velvet actually functions as a sexual stimulant or is a possible remedy for sexual dysfunction (Puri, 2010), so it awaits further scientific determination of clinical efficacy regarding its potential as a sexual stimulant.
Bivalves are a class of shellfish common around the world. Their hinged two-part shells enclose all of their organs and muscles. These marine and coastal organisms have been important sources of protein for humans for thousands of years (Pauls, 2014). Shellfish meat, particularly that of oysters, has traditionally been described as having aphrodisiac properties that enhance sexual function. Like that of many bivalves, the meat of the blood clam, Scapharca broughtonii, can be eaten raw and prepared in dishes such as Japanese sushi (Sato et al., 1987).
S. broughtonii belongs to the family Arcidae and is found along East Asia’s northwestern Pacific coast. It plays a commercially important role throughout East Asia (Yu et al., 2015). A common molecule found in the muscle extracts of S. broughtonii is N-Methyl-D-aspartic acid (NMDA). This blood clam is believed to be the first identified source containing NMDA (Sato et al., 1987). Moreover, D-aspartate, an amino acid, has been isolated from S. broughtonii (Tsesarskaia et al., 2009). This amino acid has been found to be present in numerous bivalves and snails (Shibata et al., 2001) (Figs. 25.1 and 25.2).
D-aspartate and NMDA are classified as amino acids and primary metabolites. Both are present in the neuroendocrine systems of vertebrates and invertebrates, where they contribute to the production and release of hormones (Tsesarskaia et al., 2009). NMDA is known as an agonist for some central nervous system glutamate receptors (Tarui et al., 2003). Lesser known, however, is the mechanism of action by which D-aspartate influences sexual function or the quality of spermatozoa (or both) (D’Aniello et al., 2012).
Studies have found that a correlation exists between supplementation of D-aspartate and semen concentration and semen quality in humans (D’Aniello et al., 2012). Oral doses of D-aspartate over the course of two to three months have been found to significantly improve spermatozoa count and mobility (D’Aniello et al., 2012). This in turn may improve human fertility. Due to limited populations of S. broughtonii, research into identifying new species containing D-aspartate and NMDA could be beneficial. Since bivalves have been found to be rich in D-aspartate, bivalves in the family Arcidae of North America’s coastal regions could be studied as functional foods for sexual function promotion and fertility in men.
Plants are eukaryotes and belong to the kingdom Plantae. Unlike animal cells, plant cells have cell walls composed of a polysaccharide known as cellulose, the most common organic molecule on the planet. Plants use photosynthetic processes to create food energy, and are autotrophs. Most plants appear green due to the chlorophyll pigment found in chloroplasts.
Serenoa repens, or saw palmetto, is a small shrublike palm native to the southern United States, including Florida, Mississippi, Georgia, South Carolina, and Louisiana (Anderson and Oakes, 2012). Growing in soil that is acidic, basic, moist, or dry (Anderson and Oakes, 2012), S. repens is the most abundant palm in the United States (Bennett and Hicklin, 1998). Its drupaceous fruit becomes ripe from August to October. Native Americans used multiple parts of the abundant S. repens plant. The leaves have traditionally been used to make thatched roofs and baskets (Bennett and Hicklin, 1998). In addition, various societies throughout the Americas have used palms in traditional medicine (Sosnowska and Balslev, 2009).
Focus has been increasing on using plant-based therapies to treat prostate disorders, with some of those therapies incorporating S. repens (Sosnowska and Balslev, 2009). Phytotherapeutic formulations prepared from the fruit of S. repens include liquid extracts, dried berries, powders, and tinctures (Penugonda and Lindshield, 2013). Two of the principal phytochemicals present in S. repens are its phytosterols and fatty acids (Penugonda and Lindshield, 2013). Phytosterols are found in plant cells and are cholesterol-like molecules (Ostlund, 2002). Phytosterols, particularly preparations of β-sitosterol, have been successfully used to treat symptoms of benign prostatic hyperplasia (BPH) (Higdon, 2007). The major fatty acids present in S. repens are lauric, myristic, palmitic, stearic, oleic, and linoleic (Penugonda and Lindshield, 2013) (Figs. 25.3 and 25.4).
Benign prostatic hyperplasia is a noncancerous enlargement of the prostrate. Fatty acids and phytosterols of S. repens may act to inhibit the enzyme 5α-reductase (De Monte et al., 2014). This enzyme may contribute to BPH by converting testosterone to dihydrotestosterone. Benign prostatic hyperplasia has been shown to be correlated with lower quality of life in men, which may include reduced sexual function such as by erectile dysfunction (Bruskewitz, 2003). Treatment of BPH could thus improve male sexual drive and erectile function. Although supplements and extracts from S. repens have been used in randomized clinical trials, relatively few studies have evaluated the composition of the different preparations used in the randomized clinical trials (Penugonda and Lindshield, 2013).
Studies have shown S. repens to have few side effects in treating BPH, while surgery and less invasive medical approaches can cause erectile and ejaculatory dysfunction (Orabi et al., 2011). Although few studies have evaluated the phytochemicals from various extracts of S. repens, the low reported side effects when using this botanical to treat BPH make it worthy of further study.
Damiana (Turnera diffusa) has been used by both men and women as an herbal aphrodisiac since the ancient Mayan civilization (Balch and Bell, 2012). This small to medium-sized perennial plant is native to southwestern Texas in the United States and then southward through Mexico, Central America, the Caribbean, and South America (Everitt et al., 2002). Turnera diffusa can grow up to one to two meters tall, and its leaves are generally clustered (Everitt et al., 2002). Damiana leaves contain as much as 1% volatile oil consisting of 1,8-cineole, p-cymene, alpha and beta-pinene, thymol, alpha-copaene, and calamine (Kumar and Arora, 2013).
Damiana leaves are dried to make a tisane (herbal tea) or for smoking. In addition, T. diffusa is also available in capsules and as liquid extracts (tinctures) (Balch and Bell, 2012). Damiana is on the US Food and Drug Administration’s so-called GRAS list (generally recognized as safe) and is often used as food flavoring (Kumar and Arora, 2013). The plant is found mainly in traditional herbal remedy products in combination with other botanicals such as Cola nitida (cola) and Serenoa repens (saw palmetto). Indigenous Mexican women currently make a natural herbal product by steeping 30 g of leaves into one liter of tequila for one week to obtain an aphrodisiac liquor that is reportedly consumed to enhance lovemaking (Porras, 2013).
Among various published studies on this botanical, one clinical study involving 1000 men in the United States and Europe showed that damiana can relieve erectile failure when a man attempts to repeat intercourse after an orgasm (Balch and Bell, 2012). In addition, taking a combination of damiana and the flowering plant muira puama (Ptychopetalum olacoides) has been associated with an increase of morning erections and sustained erection during intercourse (Balch and Bell, 2012). Of 77 participants in one double-blind placebo-controlled study, 34 women were given a nutritional supplement (Arginmax) containing damiana extract for four weeks, and 43 were given placebos. The women who received Arginmax showed an improvement in sexual desire, reduction in vaginal dryness, and improvement in clitoral sensation (Kumar et al., 2005). Unlike other uncontrolled studies evaluating damiana’s efficacy in women, this study utilized a control group. Thus, the findings of this study are more suggestive of damiana’s effectiveness in women who ingested this nutritional supplement.
Furthermore, an animal-based study was conducted in an effort to validate the traditional use of the plant for sexual dysfunction and impotence. A group of researchers in Italy administered a hydroalcoholic extract from the leaves of T. diffusa to sexually potent and sexually inactive or impotent rats (Arletti et al., 1999). This intervention study demonstrated that the extract had no effect on sexually potent rats but did improve the copulatory performance of the sexually inactive or impotent rats and increased the percentage of rats achieving ejaculation (Arletti et al., 1999).
Overall, however, scientific evidence that supports damiana’s so-called aphrodisiac properties is lacking; these properties have not been demonstrated in humans. However, studies evaluating damiana’s efficacy in male rats has indicated an improved sexual function (Edwards et al., 2015), making this botanical worthy of further research to better understand its use as a potential remedy for sexual dysfunction in aging humans.
Bacteria fall into two different groupings: Bacteria and Archaea. The two species we have researched are from Kingdom Bacteria. These are single-celled prokaryotic organisms, meaning their DNA is not contained in a membrane-bound nucleus. Species of bacteria can be heterotrophic (requiring complex organic compounds of nitrogen and carbon) or autotrophic (requiring only carbon dioxide or carbonates as a source of carbon). Moreover, some species from the kingdom Bacteria are useful in industries such as food production and pharmaceuticals.
Portions of the human body in contact with the external environment—skin, mucous membranes, and gastrointestinal tract—are host to an extensive variety of microorganisms known as the microbiota (Petrova et al., 2015). Establishment of the human microbiome begins after birth and largely resembles that of an adult by two years of age (Luoto et al., 2013). The human microbiota can be supplemented with so-called good bacteria through the consumption of probiotic foods—that is, foods containing live microorganisms.
Throughout human history and across cultures, people have consumed probiotic foods. The diet of many indigenous Hawaiians contains a probiotic food called poi (Brown and Valiere, 2004). Poi is made from the underground stems of the taro plant (Colocasia esculenta L.), which are called corms. Once the corms are cooked and crushed, the resulting paste is fermented with lactic acid bacteria and yeasts that naturally occur on the plant’s surface (Brown and Valiere, 2004). Poi preparations often contain several species of the genus Lactobacillus.
In recent years, the market for probiotic foods in the United States has noticeably expanded (Vanderhoof and Young, 2008). Yogurt and sauerkraut are examples of two probiotic foods common in Western cuisine. In North America, probiotics are commonly consumed as food or taken as dietary supplements to augment the gastrointestinal tract’s health and function (Vanderhoof and Young, 2008). One of the common bioactive components of many probiotic foods and supplements are species of Lactobacillus, which are rod-shaped gram-positive bacteria (Schillinger, 1999). As lactic acid bacteria, they produce lactic acid from hexose sugars (Makarova et al., 2006). This acid contributes to the taste of many probiotic foods and can have important roles in human health.
Lactobacilli are the primary microbes present in the vaginal microbiota or flora (Barrons and Tassone, 2008). One way that these species regulate the vaginal ecosystem is by lowering pH. Maintaining a low vaginal pH is important to prevent the overgrowth of pathogenic bacteria leading to infections and bacterial vaginosis, the overgrowth of undesirable vaginal bacteria (Barrons and Tassone, 2008). The processes that maintain vaginal Lactobacilli growth and pH in reproductive-aged women are altered in postmenopausal women due partly to the thinning of the vaginal wall (Hoffmann et al., 2014). In a five-year study of postmenopausal women, Hoffmann et al. (2014) found that the prevalence of bacterial vaginosis increases with age.
Low levels of Lactobacilli in vaginal microbota can be treated with the help of probiotics. Many probiotic remedies are taken orally as food or supplements, although they can also be administered locally as vaginal suppositories, capsules, or tablets. Local administration (insertion of a vaginal suppository, capsule, or tablet) allows for direct colonization and increased control in probiotic remedies (Palmeira-de-Oliveira et al., 2015). Clinical data suggest that local administration of probiotics can help promote faster treatment of bacterial vaginosis and prevent recurrence (Palmeira-de-Oliveira et al., 2015). Since there are yet few remedies of this kind available, additional research is necessary to further develop topical probiotics for vaginal flora renewal.
The prevalence of diabetes in aging US men (65 years and older) remains high at 26%, or 12 million seniors (American Diabetes Association, 2014). A meta-analysis by Agardh et al. (2011) estimates that diabetes will reach 300 million people worldwide by 2025. One complication of diabetes is vascular abnormalities that contribute to deficient blood flow into the penis and damaged blood vessels, which in turn serves as a possible explanation for the increased rate of erectile dysfunction among men with diabetes (Várkonyi and Kempler, 2014). Researchers at the Washington University School of Medicine in St. Louis have found a key mechanism that appears to contribute to the damage of blood vessels in diabetes (Dryden, 2007). Through studies utilizing rodent models, these researchers found two enzymes that have been linked to blood vessel damage: fatty acid synthase (FAS) and nitric oxide synthase (NOS) (Dryden, 2007).
These researchers conducted a study in which nondiabetic mice were genetically engineered to make FAS in all tissues except the endothelial cells lining the blood vessels (Dryden, 2007). These mice started to experience similar problems in their blood vessels as animals with diabetes. People with type 1 or type 2 diabetes have low levels of FAS or defects in the FAS enzyme (Wei et al., 2010).
Palmitoylation is the mechanism whereby NOS is modified to bind normally to endothelial cells (Dryden, 2007). In the absence of FAS, the genetically engineered mice lose NOS palmitoylation and are thus unable to modify NOS to normally interact with the endothelial cell membrane. This leads to blood vessel problems, further inhibiting angiogenesis in mice (Dryden, 2007).
Medical biologists seeking novel regenerative therapies discovered a bacterium (Bartonella henselae) that secretes a protein known as Bartonella adhesion (BadA) (Riess and Raddatz, 2007). Work is underway to study this as a potential remedy for erectile dysfunction due to the protein’s ability to regenerate blood vessels in men. Bartonella henselae is a rod-shaped bacteria formerly known as Rochalimaea henselae (Brenner and O’Connor, 1993). BadA promotes the formation of blood vessels (angiogenesis), thus making B. henselae potentially useful for application in regeneration biology (Autenrieth, 2006). BadA achieves this effect by stimulating the formation and release of host growth factors such as vasculoendothelial growth factor (Autenrieth, 2006). Further study of this bacteria could provide scientists with information about its utility as a remedy for erectile dysfunction in diabetic men after damage to blood vessels.
Fungi are heterotrophic organisms that absorb nutrients from their surroundings, which means they are saprotrophs and feed off decaying matter. Thus, in the environment, fungi have an important role in breaking down organic materials. In addition, fungi are eukaryotic organisms that range from unicellular to multicellular. Edible fungi are consumed by people around the world and have a variety of applications beyond their role as food.
In the Western world, alcohol consumption has long been associated with alleged aphrodisiac properties such as increased sexual desire (Hernandez and Alfonso, 1997). Across cultures, alcohol has occupied a variety of important niches. The ingredients and methods of its production, however, have largely varied regionally and throughout time.
Production of beer began around 6000 years ago in what is now Iraq (Schneiter, 2004). Mesoamerican cultures also engaged in the production of alcoholic beverages such as pulque, a nondistilled fermentation of the sap of Agave atrovirens, A. mapisaga, or A. salmiana (Lappe-Oliveiras et al., 2008). Distilled spirits such as tequila and mescal can also be prepared from agave plants. North American native hops (Humulus lupulus) and grapes (Vitis riparia) are among the ingredients used to make beer and wine, respectively.
Alcoholic beverages served a significant role in the religion, rituals, divination, and healing of precontact Mesoamericans (Lappe-Oliveiras et al., 2008). Traditional fermentations of alcoholic beverages, including those prepared by Amerindians, occurred spontaneously without pure (single species) cultures of yeast (Lappe-Oliveiras et al., 2008). Yeasts first began to be cultivated in pure cultures during the 1800s, with Saccharomyces cerevisiae first being isolated in Denmark (Schneiter, 2004). Saccharomyces cerevisiae and related yeast strains are currently the most commercially important yeasts (Schneiter, 2004).
Ethanol is miscible in the lipids of cellular membranes, and its effects are associated with gamma aminobutyric acid receptors and NMDA receptors in cell membranes (Gilbert, 2014). The effects of alcohol on sexual behavior have been found to be influenced by both cognitive processes and physiological action in humans (Hernandez and Alfonso, 1997). Moreover, studies have found that an individual’s acquired expectations associated with alcohol consumption may have the largest influence on its effect (Hernandez and Alfonso, 1997). This is important because expectations may vary widely from person to person or across cultures, including expectations of alcohol’s aphrodisiac properties.
Malatesta et al. (1982) found that for both men and women a positive correlation existed between blood alcohol level, orgasmic latency, and difficulty in achieving orgasm. With increased alcohol consumption, both men and women experience decreased orgasmic responsiveness both physiologically and behaviorally. However, women in an experimental study of alcohol’s influence on orgasmic response reported greater cognitive sexual arousal and enjoyment as reported in a postmasturbation questionnaire (Malatesta et al., 1982). In their review of the literature on alcohol’s influence on sexual functioning and sexual arousal, George and Gilmore (2013) concluded that the decreases in genital response are limited to acute consumption of alcohol in high doses and chronic consumption of alcohol, a finding similar to those of Malatesta et al. (1982). These findings suggest that consumption of alcohol that is not excessive or chronic may have positive effects on sexual desire. Moderate consumption of alcohol can be defined as approximately 15–45 g of ethanol per day for those aged 45–65 years and 15–30 g for those over 65 years (Ferreira and Weems, 2008). Ferreira and Weems (2008) define a standard drink as one that contains 15 g of ethanol. Further study into the effects of alcohol consumption in moderate doses and the effects of positive alcohol expectancies on sexual desire in older adults is needed.
Diabetes is classified as either type 1 (insulin-dependent diabetes mellitus) or type 2 (noninsulin-dependent diabetes mellitus) (Hong et al., 2007). As people age, chances of being diagnosed with type 2 diabetes increase (American Diabetes Association, 2014). As previously stated, global incidence of diabetes is predicted to rise (Agardh et al., 2011). Erectile dysfunction is a common complication in men caused by type 2 diabetes (Várkonyi and Kempler, 2014), affecting between 35% and 75% of men (Várkonyi and Kempler, 2014). Type 2 diabetes also can have negative effects on orgasmic and ejaculatory function and libido in males (Várkonyi and Kempler, 2014).
Some NHPs may act as therapeutic agents to improve the lifestyle of men with type 2 diabetes. The use of these natural products over a prolonged period of time also could be safer than pharmaceuticals (Hong et al., 2007). Grifola frondosa (the maitake mushroom) is a fungus native to eastern North America and is typically found near oak trees (Fischer, 2011). It is also commonly referred to as the ’hen of the woods’ (Fischer, 2011).
One study on the efficacy of maitakes in improving type 2 diabetes focused on the enhancement of insulin sensitivity by using an extract of a glycoprotein from G. frondosa known as SX Fraction in spontaneously hypertensive rats (Preuss et al., 2007). Oral consumption of SX Fraction showed enhanced sensitivity to exogenous insulin, thus suggesting that a glycoprotein extract from maitakes (SX Fraction) could be considered as an alternative method for improving insulin sensitivity. Moreover, reducing the insulin resistance associated with type 2 diabetes could improve its comorbidities (Preuss et al., 2007).
The results of this study and what we know about the association between type 2 diabetes and erectile dysfunction suggests a need for further research into the efficacy of G. frondosa as a nutraceutical.
The colloquial definition of the Protista kingdom has often been described as being the collection of all organisms that do not fit into other life kingdoms. Protists can be heterotrophic or autotrophic. Protista contains widely diverse unicellular as well as multicellular organisms. Multicellular protists do not have differentiated tissues. In addition, protists are eukaryotic organisms that contain a nucleus. Protists are found throughout the world in moist environments.
In a recent review, longitudinal studies have shown that diminished sexual function and vaginal dryness are commonly reported symptoms of postmenopausal women (Grant et al., 2015). Genitourinary syndrome of menopause (GSM) is a group of symptoms related to the decrease of estrogen and sex steroids in aging women and include genital dryness, irritation, and sexual dysfunction due to poor vaginal lubrication (Portman and Gass, 2014). Symptoms of GSM are undertreated because vulvovaginal health issues are typically not discussed by physicians with their patients (Goldstein et al., 2013). Poor vaginal lubrication can be treated with the use of sexual lubricants. A current area of research is in natural sexual lubricants derived from seaweed gels.
The earliest recorded uses of seaweed are described in Chinese literature. Seaweed-based lubricants were traditionally used for sexual intercourse. The Chinese harvested seaweed for medical use as long ago as 3000 B.C.E.; however, the practice of farming seaweed only originated within the last 400 years in Asia (Nash, 2011). Currently, red seaweeds have an economically important role throughout the world due to the presence of phycocolloids such as carrageenan (Pangestuti and Kim, 2014). Carrageenan has a variety of applications in food production as a thickener and stabilizer in dairy products, puddings, canned pet foods, imitation creams, and syrups (Buck et al., 2006; Rogers, 2011). In the United States and Canada, the red algae genus Chondrus is the primary source of carrageenans (Rogers, 2011). Chondrus crispus or irish moss, which can be found in the United States, contains kappa and lambda carrageenan (Prajapati et al., 2014) (Figs. 25.5 and 25.6).
A study in Thailand of the carrageenan-based lubricant Carraguard found that a majority of couples using this product reported increased sexual pleasure (Martin et al., 2010). The potential for carrageenan-based products to alleviate sexual dysfunction due to vaginal dryness in postmenopausal women is an avenue for research and development. Moreover, addressing the symptoms of GSM can positively influence the quality of life of postmenopausal women (Hyun-Kyung et al., 2015). An additional benefit of sexual lubricants made from the sulfated polysaccharide carrageenan is its use in preventing the transmission of disease (Buck et al., 2006). Carrageenan has been found to be inhibitory to papillomavirus infection in vitro and has potential for use as a microbicide (Buck et al., 2006). In a double-blind, randomized study, Marais et al. (2011) found that high-risk human papillomavirus prevalence was lower among compliant Carraguard users than among compliant placebo users. Carrageenan acts to inhibit viruses by preventing the entry of virions into cells and the binding of virions (Prajapati et al., 2014). Use of carrageenan-based lubricants to improve vaginal dryness and decrease infection make carrageenan an important focus for future research.
Thyroid dysfunction is a prevalent morbidity associated with aging in adults. Bensenor et al. (2012) state that treating and diagnosing hypothyroidism in aging adults is especially important because symptoms of thyroid dysfunction can be difficult to discern from the normal process of aging. More women experience thyroid issues than men, but its prevalence among all people older than 60 years was found to be 4.4% by the Framingham Heart Study (Sawin et al., 1985). Complications with thyroid function in aging adults can be associated with variations in levels of hormones that augment the function of the thyroid. Clinical diagnosis of thyroid disorders often entails measures of thyroid-stimulating hormone, triiodothyronine, and free thyroxine levels (Bensenor et al., 2012). Diagnosis of thyroid disorders among aging adults is important due to the comorbidities that are associated with thyroid dysfunction.
Many studies have found erectile dysfunction among men with thyroid dysfunctions (hypothyroidism or hyperthyroidism) to be elevated. A study designed to investigate the impact of thyroid dysfunction on sexual health by means of a Sexual Health Inventory for Males questionnaire found that men with thyroid dysfunctions were significantly more likely to have some degree of erectile dysfunction than those who did not have thyroid disorders (Krassas et al., 2008). Another study found that in the age group of 51–80 years, erectile dysfunction scores (as scored by questionnaire) were significantly better in those without thyroid disorders than in those with thyroid disorders (Veronelli et al., 2006). Although a relationship is present between thyroid disorders and erectile dysfunction, more research is necessary to determine the causes of the association.
Although not all thyroid disorders are caused by iodine deficiency, proper function of the thyroid requires optimal dietary iodine intake (Laurberg et al., 2010). Laurberg et al., (2010) also notes that severe iodine deficiency increases the risk of hypothyroidism, while moderate iodine deficiency increases the risk of both hypothyroidism and hyperthyroidism. This shows that a suboptimal intake of iodine can contribute to thyroid disorder and could potentially contribute to erectile dysfunction. A rich food source of iodine is seaweed, which concentrates iodine found in the ocean. In a study of 14 species of seaweed consumed by humans, Desideri et al. (2016) found that Laminaria digitata contained the highest concentration of iodine. Laminaria digitata is found in the northern Atlantic Ocean and is commonly distributed along the Atlantic coast of North America from Greenland to Cape Cod. This suggests that L. digitata should be further researched for use as an iodine-rich functional food. Further research could help to understand the connection between thyroid disorders and erectile dysfunction.
Natural health products derived from native North American organisms from the five biological kingdoms have the potential to improve a variety of conditions that inhibit sexual function in aging men and women. For example, erectile dysfunction has been shown to be potentially treatable by natural health products and derivative natural products. Moreover, several comorbidities associated with inhibited sexual function in older adults such as prostate health, vaginosis, and diabetes can be improved with natural health products. One weakness we discovered in our review of the current literature on natural health products for sexual function was in the paucity of clinical evidence for the efficacy of such agents. Further research is necessary to weigh the evidence as to whether compounds in organisms can influence sexual desire, for example. It is also important to understand the physiological mechanisms of the bioactive compounds that may have practical implications for the development of new therapies for sexual function and dysfunction in older adults.
Natural health products remain a commonly utilized—but understudied—source of complementary and integrative health treatments of morbidities in aging adults. The diversity of organisms in North America, including Greenland, is ideal for research into nutraceuticals that may improve sexual conditions associated with aging in adults. This ongoing research is important because of the growing proportion of older populations throughout the world, their proportionately higher rate of sexual dysfunctions, and their frequent use of natural health products alongside allopathic medications. Development of new therapies from natural health products may reduce undesirable side effects and costs in comparison with current pharmaceuticals. The bioactive compounds found in organisms may play an important role in drug discovery and thus should be a continued goal of medical research.
Thanks are due to Dr. Arul Chinnaiyan of the Department of Pathology at the University of Michigan Medical School and to Dr. Steven M. Firestine of the Department of Pharmaceutical Sciences in the Eugene Applebaum College of Pharmacy and Health Sciences at Wayne State University for their much appreciated help in critiquing earlier forms of this manuscript. All responsibility and accountability for this chapter rests solely upon the indicated authors. No funding was used to support this project.