A survey of supplement use among more than 45,000 men and women has led authors to urge doctors to increase awareness of the habits of their patients.
"These findings suggest physicians, pharmacists and other healthcare providers need to be aware of the conditions their patients may be self-treating," said study author Dr Jessie Satia-Abouta, of the Department of Nutrition at the University of North Carolina at Chapel Hill, US.
Satia-Abouta and colleagues studied data from a 24-page questionnaire on supplement use that was completed by 45,748 men and women aged 50 to 75 in Washington state who are participating in the VITamins And Lifestyle study, a study examining associations between supplement use and cancer risk. Those surveyed supplied information on their vitamin and mineral supplement use, as well as information on their diet, physical activity, medical history and demographic characteristics.
The researchers found that more than 75 per cent of participants regularly took a supplement. More than half of the participants were taking a multivitamin and the most popular single supplements were vitamins E and C, calcium, folate and selenium. Supplement use was most popular among participants who were older, female, highly educated, Caucasian or Native American, and who had a normal body weight.
Participants with medical conditions reported using more supplements than those who did not have the medical conditions, and in some cases the supplements they chose were in line with recommendations by the mainstream or scientific press. For example, participants with coronary artery disease were more likely to report taking vitamin E and folate, and those with high cholesterol were more likely to take niacin. However, participants with prostate cancer and osteoporosis were not more likely to take selenium and calcium, respectively, which have also been suggested as potentially helpful.
In general these findings, along with previous findings, "suggest that the public may be using dietary supplements to treat illnesses," Satia-Abouta said. The study results are published in the January issue of the American Journal of Preventive Medicine.
In some cases, participants' choice of supplement may reflect misinformation. For example, male participants who reported being diagnosed with an enlarged prostate, but not prostate cancer, were more likely to take selenium. Preliminary studies suggest selenium may reduce the risk of prostate cancer, not enlarged prostate.
"Healthcare providers need to make sure their patients know what supplements they should be using and ensure they are not taking harmful doses," Satia-Abouta said.
Another finding involved gender: Although women used more supplements overall, men with medical conditions such as depression and coronary disease used more supplements than women did.
"This suggests women may tend to use supplements more broadly and for disease prevention while men may choose to use a supplement only after diagnosis of a condition," Satia-Abouta said.
The researchers pointed out several study limitations. One is that the nature of their study did not allow them to determine whether participants started taking supplements before or after being diagnosed with a medical condition. "We cannot conclusively establish whether participants in our study are using supplements to treat illnesses or prevent future disease," Satia-Abouta noted.
The study was supported by a grant from the US National Cancer Institute.