January 4, 2013
Dear Mayo Clinic:
Is it true that a large study found that most vitamin supplements may actually do more harm than good? What supplements should I avoid? Which are worth taking? I am 67 and in good health.
Advice on vitamin and mineral supplementation is constantly changing. Over the past few years, well-conducted research has found that some supplements previously thought to be beneficial for disease prevention may not be helping — and some may actually be causing harm.
This research includes the Iowa Women's Health Study, which tracked the supplementation habits of more than 38,000 women 55 and older for nearly 20 years. Among the findings, taking a multivitamin appeared to increase risk of premature death. Interestingly, the people who took multivitamins actually had better overall health habits than those that didn't.
With this study and others, there is increasing evidence against taking most supplements for general health or disease prevention. There are exceptions — such as calcium and vitamin D for bone health — but even the exceptions should be approached with caution.
Many people take supplements as an "insurance policy" against inadequate nutrition. However, in developed countries, deficiencies in most vitamins and minerals are uncommon, unless there is a predisposing condition. Taking supplements provides these nutrients far in excess of what's necessary for good health.
Another reason people take supplements is to help prevent serious diseases. Studies have consistently shown that diets high in antioxidant-rich fruits, vegetables and other plant foods are associated with lower rates of cancer and heart disease. However, studies looking at supplements, including antioxidants such as beta carotene and vitamins A and E, haven't shown much benefit and there is some evidence they may actually cause harm.
Plant foods contain hundreds of beneficial compounds termed phytonutrients. Singling out a few specific vitamins as being beneficial appears to be too simplistic. Also, some vitamins occur in many forms — and supplements may not provide the right forms in the right amounts.
Potentially risky vitamin and mineral supplements include:
Vitamin E — A 2012 review of research published in the Cochrane Database found that taking daily vitamin E supplements may increase the risk of dying prematurely.
Vitamin A — The same review found large doses of vitamin A supplements were also associated with an increased risk of dying prematurely. Supplementation with beta-carotene, a compound that's converted to vitamin A by the body, was also shown to increase risk of death, especially for smokers or former smokers. Since vitamin A deficiency is rare in the U.S., it's probably not worth the potential risk to take this supplement.
Folic acid (vitamin B-9) — Most older adults consumeadequate folate. Supplementationhelps prevent birth defects, but evidenceof other benefits has beenelusive.
Vitamin B-6 — Large daily doses of vitamin B-6 — more than 100 milligrams (mg) — can over time cause nerve damage.
Vitamin B-3 (niacin) — High doses can help lower high cholesterol levels, but this should be done only under the supervision of a doctor. Side effects, including severe liver disease, can occur.
Iron — In healthy men and postmenopausal women, iron deficiency is rare. If you're in one of these categories and iron deficient, further evaluation may be considered. There is some evidence that too much iron is associated with adverse effects, including possibly increased mortality.
Trace minerals — Copper, chromium, magnesium, selenium and zinc are among the essential trace minerals. However, there isn't any solid evidence that trace mineral supplementation has any benefit in the absence of deficiency — which is rare.
Supplements that older adults may consider taking include:
Calcium — The recommended intake is 1,200 mg daily for women over the age of 50 and men over the age of 70. A meta-analysis found that calcium supplementation increased the risk of cardiovascular disease. However, not all studies have supported this conclusion. Mayo Clinic experts support meeting — but not exceeding — your daily calcium requirements, primarily through food, as there was no evidence of increased risk with dietary sources of calcium.
Vitamin D — In support of bone health and prevention of falls, 600 to 800 IU daily from diet and supplements combined is recommended for older adults. Some doctors and organizations believe that higher doses may be appropriate. Vitamin D enhances calcium absorption.
Vitamin B-12 — It's estimated that up to 15 percent of older adults are deficient in vitamin B-12. Since vitamin B-12 has not been shown to cause harm, even in large doses, it may be beneficial for older adults to take a B-12 supplement containing at least 2.4 mcg — the Recommended Dietary Allowance — to help prevent deficiency.
Although many of the reported risks are small, any increase in risk is troublesome since people take supplements to improve their health. Because a large number of people take supplements, a correspondingly large number may experience adverse effects. Talk to your doctor before taking any supplements or making any changes to your current regimen, and ask for his or her recommendations for your specific needs.
— Donald Hensrud, M.D., Preventive, Occupational and Aerospace Medicine, Mayo Clinic, Rochester, Minn.