Risks in mega-vitamin dosing?
|Dr. Bob Anderson|
Ask The Pharmacist
By Dr. Bob Anderson
In the United States, there is widespread use of dietary supplements by 53 percent of adults, including almost 39 percent of us consuming multivitamins.
As consumers we pay more than $28 billion dollars annually for diet supplements. Are the use and cost justified? A recent editorial, accompanied by new studies published in the prestigious Annals of Internal Medicine, questions widely held beliefs that diet supplements and vitamins improve health.
The most common antioxidant vitamins recommended included vitamin E, vitamin C and beta carotene (vitamin A). There was a strong movement in the 1990s promoting the use of large doses of antioxidant vitamins to prevent or, at least, reduce the risk of heart disease, cancer and other chronic illnesses. The U.S. Preventive Services Task Force concludes there is “limited evidence” to support these claims.
Show me the science
One study followed male physicians, age 65-plus, who took multivitamins for 11 years; their results showed vitamins had no effect on cognitive decline. A more recent study found high-dose vitamins had no effect on heart disease in those patients who were heart attack survivors. Earlier studies suggest antioxidant vitamins may interfere with statin therapy, negating some of its benefits in treating heart disease.
The Heart Outcomes Prevention Evaluation (HOPE) study, which followed almost 10,000 patients at high risk of heart attack or stroke for 4 1/2 years, found participants taking 400 IUs/day of natural vitamin E experienced no fewer cardiovascular events or hospitalizations for heart failure or chest pain than participants taking a placebo.
In the HOPE-TOO follow-up study, almost 4,000 of the original participants continued to take vitamin E or a placebo for an additional 2 1/2 years. HOPE-TOO found vitamin E provided no significant protection against heart attacks, strokes, unstable angina or deaths from cardiovascular disease or other causes after seven years of treatment. Participants taking vitamin E, however, were 13 percent more likely to experience – and 21 percent more likely to be hospitalized for – heart failure, a statistically significant, but unexpected, finding not reported in other large studies.
Additional risks of high-dose vitamins
The most recent published clinical trial of vitamin E and men's cardiovascular health included almost 15,000 healthy physicians age 50, more or less, who were assigned randomly to receive 400 IUs of synthetic vitamin E every other day, 500 mg of vitamin C daily, both vitamins or a placebo.
During a mean follow-up period of eight years, intake of vitamin E (and/or vitamin C) had no effect on the incidence of major cardiovascular events, myocardial infarction, stroke or cardiovascular mortality.
Furthermore, use of vitamin E was associated with a significantly increased risk of hemorrhagic stroke.
In postmenopausal women, studies of antioxidant vitamins have demonstrated equivocal results – some positive, some negative. Outcomes using vitamins to prevent cancers have been equally disappointing. Some studies even have reported some antioxidants may increase the risk of cancer in smokers and prostate cancer in men.
Who needs vitamins?
Prenatal vitamins during pregnancy provide added required nutrients and prevent birth defects. Women with heavy menstrual bleeding may benefit with a multivitamin with iron. Vegetarians may be deficient in several B vitamins. Those at risk of macular degeneration may benefit from antioxidant eye vitamins that have proven effective. As we get older, many of us cannot absorb efficiently certain vitamins, so maybe a Centrum Silver or equivalent is indicated. I still take a little extra vitamin C when coming down with a cold.
Designing a strong research study on the potential benefits versus risks of high dose vitamins is a difficult task due to many variables. Which vitamins (natural or synthetic), at what doses, for how long, for men or women, healthy patients or those at risk, young or old, ethnic differences, interactions with other lifestyles, such as diet, exercise, smoking, etc.? I think you can appreciate the difficulty of designing a clinical trial.
The bottom line is: Do not use high-dose vitamins (and minerals), unless prescribed by your doctor, until more science is known. They may do more harm than good. If you have a decent diet, high in vegetables and fruits, you probably are ingesting the recommended daily allowances of most vitamins in their natural state. If not, a daily multiple vitamin will not be harmful and may be helpful.
Bob Anderson is professor emeritus from Mercer University, a sometime pharmacist at Walgreens Pharmacy in Jasper and a full-time resident of Big Canoe.