Multi-vitamin pills are linked to breast cancer: research

The shock finding has rattled Australia's $2.5 billion complementary health industry, which is urging consumers not to panic, News Ltd says.

In a 10-year study of more than 35,000 women, researchers discovered those who regularly took a multi-vitamin pill increased the risk of developing a tumour by 19 per cent.

They said the result was concerning and needed investigation as many women use multi-vitamins in the belief they prevent chronic diseases such as cancer. A "biologically plausible" explanation is that taking vitamin and mineral supplements significantly increases the density of breast tissue, a strong risk factor for breast cancer. Folic acid, often present in a potent form in multi-vitamins, may also accelerate tumour growth.

The study, conducted by Sweden's Karolinska Institute and published in the American Journal of Clinical Nutrition, has been greeted with interest and caution by Australian experts. Women who took a multi-vitamin pill in the study had higher breast tissue density than those who took no vitamin supplements.