Unclear if Multivitamins Prevent Cancer and Heart Disease

USPSTF concluded that evidence is insufficient that multivitamins prevent cancer or heart disease

(RxWiki News) It’s estimated that about half of all adult Americans take some type of dietary supplement. As a nation, we spend nearly $12 billion each year on vitamin and mineral supplements. But do these supplements help prevent our most daunting diseases?

A systematic review of the latest research has concluded there is not enough evidence that vitamin and mineral supplements prevent cancer, heart disease or death.

Two studies did show that multivitamin supplementation offered men some protection against cancer, but not women.

"Tell your doctor about all the supplements you’re taking."

This review was conducted by researchers to update the 2003 United States Preventive Services Task Force (USPSTF) recommendation that concluded there was insufficient evidence to recommend for or against the use of vitamins A, C and E, multivitamins with folic acid or antioxidant combinations for the prevention of cardiovascular disease (CVD) or cancer.

At that time, the USPSTF did recommend against the use of beta-carotene supplements (alone or in combination with other vitamins) because research had found they could harm individuals at high risk for lung cancer, including smokers.

The current review included 26 studies that evaluated the benefits and harms of using vitamin and mineral supplements to prevent cancer, CVD and all-cause mortality (death from any cause).

All of the studies involved adults with no known nutritional deficiencies.

Two researchers reviewed the high- or good-quality studies on the effects of vitamins A, B1, B2, B6, B12, C, D and E, calcium, iron, zinc, magnesium, niacin, folic acid, beta-carotene and selenium. These studies evaluated single, paired and combinations of three or more vitamins and minerals.

The term “multivitamin” was defined as a supplement that combined vitamins and minerals.

Pooled results of five multivitamin studies found no effect on all-cause mortality or CVD.

One of these studies — the Physicians’ Health Study II involving 14,641 US male physicians — found a reduced overall cancer risk after 11.2 years of follow-up.

The SUpplementation in Vitamins and Mineral AntioXidants Study (SU.VI.MAX), which included 13,017 men and women, found that multivitamin use did not impact overall cancer incidence after an initial 7.5-year follow-up or an additional five-year post-treatment follow-up. When the data was analyzed by gender, however, SU.VI.MAX found a 31 percent reduced cancer risk in men, but not in women.

The reviewed studies reconfirmed the potential harms of beta-carotene supplementation on lung cancer incidence and death for individuals at high risk for lung cancer.

The authors concluded, “We found no consistent evidence that the included supplements affected CVD, cancer, or all-cause mortality in healthy individuals without known nutritional deficiencies.

The researchers cautioned that the results should not be overgeneralized, and that more research is needed to examine the benefits of multivitamin supplements.

dailyRx News spoke with Brian D. Lawenda, MD, National Director of Integrative Oncology and Cancer Survivorship, 21st Century Oncology and Founder of IntegrativeOncology-Essentials.com, about this study.

"Researchers and food scientists are almost all in agreement that in large part due to poor dietary choices and inadequate consumption of foods with high nutritional quality, a large percentage of the US population is deficient in multiple micronutrients (vitamins A, B6, B12, C, D, E, magnesium, zinc, etc.),” Dr. Lawenda explained.

“We have known for years that micronutrient deficiencies increase one's risk of developing various diseases (i.e., CVD, osteoporosis, cancer, etc.), impaired immunity and accelerated aging,” he continued. “So, why is the USPSTF telling us that taking a multivitamin (MVI) supplement is ineffective in helping to promote healthful outcomes (e.g., CVD and cancer)?

"Simply put, thanks to numerous study design flaws this panel of experts can’t say definitely whether taking an MVI is able to reduce chronic diseases in otherwise healthy individuals,” Dr. Lawenda said.

He pointed out that the MVIs studied had various compositions and doses, some of which may be unsafe; that there were no controls (people who did not take the supplements); that questionnaires were used instead of testing blood levels; and participants included healthy people who generally have better lifestyles.

“For example, many MVI’s contain iron, however most healthy adults do not need supplemental iron (a free radical producing micronutrient). It has been postulated that iron supplementation may increase the risk of CVD and cancer,” Dr. Lawenda said.

He continued, “All of these issues — and many others — make analyses of MVI studies confusing at best. In light of the fact that most of us do not consume diets with the full complement of all of the micronutrients we need to support optimal health, I often recommend to my patients that they consider taking a high quality MVI using micronutrient dosages that meet the latest recommended daily allowances established by the Food and Nutrition Board of the US Institute of Medicine."

This study was published November 11 in the Annals of Internal Medicine.

The Agency for Healthcare Research and Quality funded this research.

Several of the authors have received research funding from the Agency for Healthcare Research and Quality. No other conflicts of interest were disclosed.

Review Date: 
November 11, 2013