Because there are nutrients that you require as you get older to keep your body healthy and disease-free, many people turn to the supplement industry—with sales hitting $23.7 billion in 2007.

Despite this, research continues to be divided on whether individual supplements improve longevity, are harmful, or are simply excreted right out of your body.

So, What Should You Do for a Longer, Healthy Life?

First of all, remember that the best source of any ingredient is food. Diets rich in beta-carotene have been associated with a lower risk of cancer, for example, but the same protective effect was not found with beta-carotene supplements. Here are some supplements commonly taken for longevity and the research associated with them:

Calcium: This mineral keeps bones strong and is necessary for muscle and nerve function and blood transport. In a 2011 review of the Iowa Women’s Health Study, in which 38,000 older women were tracked over a 22-year period, calcium was the only common multivitamin component shown to have a positive effect on mortality—that is, those women taking calcium (average 400-1300 mg/day) had a slightly lower risk of dying during that time.

By contrast, other reviews of longitudinal or long-term studies have suggested that taking calcium supplements can increase the risk of heart attack and stroke in women. In light of conflicting research, it’s best to talk to your doctor about the safety of calcium supplements.

Vitamin D: Vitamin D works with calcium to keep bones healthy; it may also help protect against certain cancers and other diseases.

It’s synthesized in skin in the presence of UV light, so concerns have been raised about whether people living in northern climates with reduced daylight in winter can get enough. A 2007 review of more than 57,000 participants, in 18 separate research trials, concluded that a safe level of vitamin D supplementation (400-600 IU) did enhance longevity, either by reducing the incidence of certain cancers and cardiovascular disease, or by improving survival in patients with these conditions.

By contrast, a 2013 study of more than 9,000 participants in the Canadian Multicentre Osteoporosis Study (CaMos) found neither harm nor benefit to mortality associated with vitamin D intake over a 10-year period.

Vitamin B6: Vitamin B is involved in the creation of neurotransmitters and blood cells, and regulating levels of an amino acid called homocysteine. Because B vitamins like folic acid, B6, and B12 have been shown to lower homocysteine levels—a status associated with a lesser risk of heart disease and stroke—researchers have investigated whether supplementation would help prevent these conditions and improve longevity.

In several large-scale studies, however, these B vitamins as supplements had no effect on the incidence, or severity, of heart disease or stroke. Similarly, in research examining the effect of B6 supplements on the incidence of cancer, no effect on mortality was found.

Vitamin B12: People over the age of 50 may not absorb vitamin B12—required for blood and nerve health—as effectively. Previously, it was believed that vitamin B12 (like B6) supplementation, especially when combined with folic acid, could help ward off heart disease and stroke, but that has largely been discounted. Research is ongoing to see if vitamin B12 can help treat or prevent dementia, which could in turn promote longevity.

Vitamin C: Necessary for the manufacture of collagen and certain neurotransmitters, Vitamin C is also a powerful antioxidant. A 2009 study of more than 77,000 people, between the ages of 50 and 76 years, found that non-smokers who took about 300mg of vitamin C for 10 years were 24 percent less likely to die during that time period; however, no longevity benefit from taking vitamin C was found for smokers in this group. Research is ongoing to determine whether vitamin C will help prevent certain cancers and cardiovascular disease.

Selenium: A trace mineral, selenium is used to form antioxidant enzymes in the body. Antioxidants mop up the harmful byproducts of cell metabolism and environmental toxin exposure. Selenium levels in populations vary according to the concentration of the mineral in soil where food is grown. A 2008 review of almost 14,000 participants in the United States found a non-linear relationship between levels of selenium in the blood and mortality—that is, low levels of selenium were associated with higher mortality, as were high levels. Most studies have considered supplements in the range of 100-200mcg; federal dietary guidelines suggest that adults over the age of 19 should consume daily totals of 55 mcg/day, not to exceed 400 mcg/day.

Beta-carotene: A form of vitamin A found in colorful fruits and vegetables, diets rich in beta-carotene have been associated with a lower risk of cancer. Studies into beta-carotene supplements have not shown the same results; some have actually indicated an increase in mortality. There is no recommended daily allowance (RDA) for beta-carotene.

Supplement research faces challenges in terms of sorting out other lifestyle factors (or "confounding" aspects) like smoking, likelihood of getting screened for diseases, diet, and exercise. It will probably be some time before science tells us with certainty which vitamins and minerals can help extend our lives, and by how much. Don’t despair. Remember that many studies have shown that a plant-based Mediterranean-style diet, with lots of fruits and vegetables that are high in fiber, delivers on the necessary nutrients for most people.

Make sure you consult your physician or nutritionist before taking any supplements. More is not better, so don’t megadose. Vitamins and minerals from all sources (fortified foods, multi-vitamins, single-vitamin products) add up. They can also interfere with medication you may be taking and can be dangerous for people with certain medical conditions.

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