How Much is Too Much?

Excess Vitamins and Minerals in Food Can Harm Kids’ Health

June 19, 2014

How Much is Too Much? : Vitamin supplementation trials underscore potential risks

Recent experiments with vitamin supplementation have also illustrated the dangers of excessive vitamin intake and shown that supplements are generally ineffective for preventing deaths or disease due to major chronic diseases (Fortmann 2013; Guallar 2013; U.S. Preventive Services Task Force 2014). 

In several clinical trials, participants who took elevated amounts of β-carotene, vitamin E and vitamin A actually had a higher risk of cancer and higher mortality than a control group (Omenn 2007). One study, the beta-Carotene and Retinol Efficacy Trial, tested the effect of daily doses of β-carotene (30 mg) and retinyl palmitate (25,000 IU) on cancer incidence in 18,314 participants at high risk of lung cancer because of a history of smoking or asbestos exposure. This multi-center trial, sponsored by the Fred Hutchinson Cancer Research Center and the National Cancer Institute, began in 1985 and was halted in January 1996, 21 months ahead of schedule. It was stopped because of a clear link between vitamin intake and cancer incidence and mortality ( 2012). Participants who took the vitamins had a 28 percent higher lung cancer incidence, 17 percent more deaths overall and a higher rate of heart disease deaths than those who took a placebo (Goodman 2004). 

Similarly, the Selenium and Vitamin E Cancer Prevention Trial, conducted by the National Cancer Institute at 427 participating sites across the United States, Canada, and Puerto Rico, found no beneficial effect of selenium supplementation on prostate cancer risk, and instead found a 17 percent increased risk from taking vitamin E (Kristal 2014). In this study of 1,739 men with diagnosed prostate cancer, participants took 200 micrograms of selenium and 400 IU of vitamin E daily, either separately or in combination. This trial was also stopped once the data revealed there was no protective benefit for selenium and an increased risk of prostate cancer among those taking vitamin E. The researchers concluded that men should avoid selenium or vitamin E supplementation at doses above the recommended dietary intakes.


Even high exposure to folic acid, which is legally required to be added to flour and flour products in the United States to prevent fetal developmental defects, has been linked to unanticipated risks such as childhood allergy and asthma and elevated cancer risk (Brown 2014; Castillo 2012). In a study in Norway, where folic acid is not added to food, treatment with folic acid plus vitamin B12 was associated with higher cancer rates and all-cause mortality in patients with ischemic heart disease (Ebbing 2009).

In Australia, a study found that consuming synthetic folic acid was statistically associated with colon polyps in older men (Lucock 2011). A March 2014 study by the Roswell Park Cancer Institute in Rochester, N.Y., found an increased risk of breast cancer among European-American women who ingested the most synthetic folate from fortified foods. In contrast, eating foods naturally high in folate was associated with lower breast cancer risk (Gong 2014). In animal studies, folic acid has accelerated progression of mammary tumors (Deghan Manshadi 2014).

In summary, a variety of studies designed to investigate whether high vitamin doses could prevent disease have demonstrated that excessive intake can instead be harmful. These findings lend urgency to the need to protect young children from excessive vitamin and mineral supplementation.