Dietary supplements: Risk to older women

11th October 2011 - A new study suggests several commonly used vitamin and mineral supplements may be doing older women more harm than good.  

The benefits of a proper diet on our health have been known for years. Although a healthy diet provides sufficient amounts of vitamins and minerals, it's estimated more than a third of adults in high income countries regularly take supplements hoping to further improve their health and prevent diseases.

The study

Using data collected from a study of women in the US state of Iowa, Jaakko Mursu, of the University of Eastern Finland and the University of Minnesota, US, and colleagues, examined  the association between vitamin and mineral supplements and death rate among 38,772  women with an average age of 61.

Supplement use was self-reported in 1986, 1997 and 2004 through questionnaires.

The findings

The authors found that supplement use increased substantially between 1986 and 2004, with 62.7% of women reporting use of at least one supplement daily in 1986, 75.1% in 1997 and 85.1% in 2004.

They also concluded that the use of most supplements was not associated with reduced mortality in older women, and many supplements appeared associated with increased mortality (death) risk.

After adjustment, use of multivitamins, vitamin B6, folic acid and the minerals iron, magnesium, zinc and copper, were all associated with increased risk of death in the study population.

The association between supplement intake and mortality risk was strongest with iron, with progressively lower doses being associated with increased risk as the women became older.

Conversely, calcium supplements appear to reduce the risk of mortality.

Findings for both iron and calcium supplements were repeated in separate, short-term analyses with follow-up occurring at four years, six years and 10 years. The study is published in the Archives of Internal Medicine.

More harm than good

"Based on existing evidence, we see little justification for the general and widespread use of dietary supplements", the authors conclude, unless doctors have recommended certain supplements to individual patients.

In an invited commentary, Goran Bjelakovic of the University of Serbia and Christian Gluud, of Copenhagen University Hospital, Denmark, write:  "Dietary supplementation has shifted from preventing deficiency to trying to promote wellness and prevent disease. Until recently, the available data regarding the adverse effects of dietary supplements has been limited and grossly underreported."

They say the phrase "more the better" is wrong and conclude: "We cannot recommend the use of vitamin and mineral supplements as a preventive measure, at least not in a well-nourished population."

UK advice

The NHS says most people should be able to get all the nutrients they need from a varied and balanced diet. It already cautions that if people choose to take vitamin and mineral supplements, taking too much or taking them for too long can cause harmful effects. 

The Department of Health says all people aged 65 and over may benefit from taking vitamin D supplements.