Multivitamins & breast cancer



The multivitamin pill is a favourite supplement of people who are “well and would like to stay that way”. They are usually taken as insurance so they know they are getting all the main nutrients each day.

Big study hints at problem

Vitamins and minerals are found in a range of foods so they are considered “natural”, but taking large doses in a tablet form is quite unnatural and this is rarely mentioned. Before vitamin supplements became popular in the 1970s there were no studies indicating they were safe because it was assumed that natural = safe. Most scientific reviews have shown little advantage for general health when taking specific vitamins or multivitamins, partly because those that take them are both moderately well-off and moderately well.

A Swedish study of over 35,000 women who were tracked for 10 years has indicated that taking a multivitamin could increase the risk of breast cancer. Multivitamin use was associated with a 19% increase in the risk of breast cancer. Women who had taken multivitamins for more than three years had a 22% increased risk. Those who took calcium tablets had a decreased risk of breast cancer. Other studies have shown a link between multivitamin supplements and breast cancer, while others haven’t, so there is no clear direction yet.

Some supplements useful

We do know that supplements may be helpful in specific circumstances. Pregnant women are told to take folate and iron because their increased needs can be tough to get by food alone. Calcium supplements can be helpful to those who aren’t big fans of dairy food. With possibly one third to one half of Australians being vitamin D deficient during winter means a vitamin D supplement. or more midday sun, is required. Vitamin supplements may also be useful for backpackers relying on a limited range of food or during long periods of illness.

What does it all mean?

If you look after yourself, there is probably no advantage to taking a multivitamin for a shot-gun spray of nutrients. If you prefer to take one, then chose one that provides the vitamins and minerals in amounts equal to the daily needs (Recommended Dietary Intake – RDI) or less. The perfect multivitamin would provide about 30-50% of the RDI, but this is not great for marketing – people like to see bigger numbers, so many supplements provide much more than is required leading to the “expensive urine” comments.

Please remember one really important thing: by taking vitamin supplements you are part of a giant experiment. There is a lot we don’t know about the long term effects of supplements. Don’t be surprised if more research shows that taking vitamins as a supplement in doses more than is required could be harmful down the track. The best evidence for a long life is to eat well.

Reference: American Journal of Clinical Nutrition. 2010; 91: 1268- 1272

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