In fact, as of 2017, 70% of older adults reported using at least one dietary supplement. A full 54% reported taking two supplements and 29% reported taking four or more supplements. The most frequently used supplements were multivitamins, Vitamin D, calcium, and omega-3s. At least 9% also reported using an herbal/botanical product, a number that is likely to have increased since the time of this survey [2].

In fact, as of 2017, 70% of older adults reported using at least one dietary supplement. A full 54% reported taking two supplements and 29% reported taking four or more supplements. The most frequently used supplements were multivitamins, Vitamin D, calcium, and omega-3s. At least 9% also reported using an herbal/botanical product, a number that is likely to have increased since the time of this survey [2].

Most older adults are also aware of changes to their cardiovascular system. As the body ages, cardiac output decreases, along with resting and maximal heart rate. Conversely, systemic vascular resistance increases, which leads to increased blood pressure. The cardiovascular system in general has a reduced response to stress and a reduction in baroreceptor activity. Many older adults also have high levels of cholesterol. These changes increase the risk for various adverse cardiovascular outcomes, as well as an increased likelihood for cardiovascular adverse effects from medications and natural products [3].

For example, sedative medications are a concern in older adults and should be used with caution. Many natural products are known to have clinically significant sedative effects and should thus be used with caution. Some common examples include kava, hops, passionflower, and valerian [8]. Anticholinergic medications are also considered to be of high concern in older adults. Some natural products, including bitter yam, European barberry, muira puama, and scopolia, have potent anticholinergic effects [9].

As mentioned, natural products are metabolized by many of the same enzymes involved in drug metabolism. Patients with liver disease may require lower doses, and natural products that have been associated with hepatoxicity should be avoided completely. These include some relatively well-known supplements, such as green tea extract, kava, garcinia, ephedra, turmeric, red yeast rice, and black cohosh [10].

Certain natural products have demonstrated clinically relevant antiplatelet or anticoagulant effects. In patients requiring the use of antiplatelet or anticoagulant medications, these products should be avoided. Some examples include garlic, ginseng, ginkgo, high doses of vitamin E or fish oil, and many others [12].

The safety of taking doses that are much higher than the DV depends on the specific nutrient in question. Fat-soluble vitamins, which are stored in the body, can cause toxicity over time. These include vitamins A, D, E, and K. Water-soluble vitamins are typically eliminated by the kidneys when quantities exceed physiological needs. Thus, toxicity is much less likely when these vitamins are taken in large quantities.

Another consideration that is not often addressed with multivitamins is the potential for reduced or enhanced absorption of various micronutrients in the presence of other micronutrients. For example, vitamin C (ascorbic acid) can increase the absorption of chromium and iron [16,17]. The presence of vitamin D increases the absorption of calcium in the intestine [18]. Iron and zinc can interfere with each other's absorption when taken on an empty stomach [19,20]. Thus, it can be difficult to predict the actual benefits and risks with these products, particularly in patients with specific nutritional needs or medical conditions.

The recommended daily intake for vitamin B12 is the same for all adults, regardless of age. However, as humans age, their ability to absorb vitamin B12 from the intestinal tract decreases. Additionally, many older adults take medications that have the potential to further reduce the absorption of vitamin B12. Some examples of these medications include metformin and proton pump inhibitors (PPIs), such as pantoprazole and omeprazole [22,23]. Due to this reduced absorption, it is recommended that older adults consume fortified foods, such as breakfast cereal. However, some may also require vitamin B12 supplements to meet their needs [24].

The recommended intake of calcium is [13]:

However, some older adults may be at increased risk for magnesium deficiency due to the use of certain medications. The most important culprits are diuretics and PPIs. For diuretics, loop diuretics are the greatest cause for concern. This risk increases when taken with other magnesium-depleting drugs like PPIs. For patients taking PPIs long-term, the FDA recommends checking serum magnesium levels at baseline and annually thereafter. Although some patients may need to discontinue the PPI permanently, others with hypomagnesemia can take a PPI and magnesium supplement concurrently [29].

Most people will be able to meet their dietary fiber needs by increasing their intake of certain foods, such as oatmeal, whole wheat cereals, and grains. However, some patients may wish to take a fiber supplement as well. Most of the popular fiber supplements on the market contain blond psyllium (Plantago ovata), which is a water-soluble fiber that has shown benefits for constipation, coronary heart disease, hyperlipidemia, and diabetes. In these studies, patients typically consumed 10–20 grams of supplemental psyllium daily [32].

There are many protein supplement products on the market. The majority of these products use whey protein, which is derived from milk [34]. Other products use pea protein or soy protein. All three of these are considered complete proteins, meaning they contain all essential amino acids, which are amino acids that cannot be made by the body and must be obtained from the diet. Collagen is also becoming popular as a protein supplement. It is important to note that all collagen protein products are derived from animals and that collagen is not a complete protein [35]. Older adults should not rely on collagen protein supplements as a primary source of protein in the diet.

Omega-3 fatty acids are generally considered "healthy fats" and are found in high concentrations in the human brain, retina, and spermatozoa. The reason that these are popular for cardiovascular health ties in to multiple purported and confirmed benefits. However, research has identified significant differences between the benefits of fish oil supplements and fish oil obtained from dietary intake of fish.

The most popular supplements for joint health are glucosamine and chondroitin, often taken together in a combination product. Glucosamine is an amino sugar that occurs naturally in humans. It is necessary for the synthesis of glycoproteins, glycolipids, and glycosaminoglycans. These compounds are found in tendons, ligaments, cartilage, synovial fluid, mucous membranes, blood vessels, heart valves, and structures of the eye. There are multiple forms of glucosamine available on the market [70]. Glucosamine sulfate is the most common form. This form must be created semi-synthetically in a lab. Glucosamine hydrochloride is the second most common form. This salt occurs naturally and can be obtained from shellfish, fungi, or corn via a simple extraction process. N-acetyl glucosamine, the acetylated derivative of glucosamine, is the least common form found in supplements [71].

Some supplements contain intact collagen, often either collagen type I, II, or III. However, much more often, collagen supplements contain hydrolyzed collagen, or collagen peptides, that are derived from these intact forms of collagen. This is also sometimes referred to on labels as collagen hydrolysate.

Vitamin E is one of the most popular vitamin supplements for dementia and cognitive impairment. In fact, there is some evidence to show that taking vitamin E can modestly slow cognitive function decline in patients with Alzheimer disease. However, it does not seem to prevent the onset of Alzheimer disease or prevent cognitive decline in general. Thus, the WHO recommends against the use of vitamin E for prevention [86].

Huperzine can cause cholinergic side effects such as dizziness, sweating, insomnia, nausea, vomiting, and diarrhea. However, it is generally well tolerated by most adults.

Alpha-L-carnitine is an ester of L-carnitine, which is an amino acid derivative that is found naturally in the body. It is made in the brain, liver, and kidneys, and the body can convert it to and from L-carnitine as needed. Alpha-L-carnitine is structurally similar to acetylcholine, which has led to interest in its use for dementia and mild cognitive impairment. Small clinical studies show that taking 1.5–2 grams daily for three months can improve some measures of cognitive function in older adults with mild cognitive impairment [105,106]. Similarly, small clinical studies show that taking 1.5–3 grams daily for three to 12 months can slow the rate of Alzheimer disease progression and improve some measures of cognitive function [107].