A diet packed with vitamin D combined with high levels of sunlight could reduce the risk of breast cancer in women by 43 per cent.
A study of 70,000 women conducted over ten years revealed that a diet high in vitamin D had no effect on its own. One theory is that consuming a diet rich in vitamin D makes a difference only when there is already a sufficient amount produced from sun exposure. Therefore, when sun exposure is low, diet intake does not make any difference to risk of disease.
However, the study concludes that an increase in overall vitamin D intake should be encouraged, including fortifying foods with it — a practice already under way in the US.
Slowing down cancer cells
Laboratory studies have suggested that vitamin D may have a number of anti-cancer effects and has been shown to slow the spread of cancer cells.
The Centre for Research in Epidemiology and Population Health in France tracked 67,721 women aged 41 to 72 for a decade to see who developed breast cancer. Their diets and ultraviolet levels where they lived were then analysed to calculate the risks. At the end of the ten-year period, 2,871 cases of breast cancer had been diagnosed.
Some 45 per cent of their dietary vitamin D came from fish and seafood, 16 per cent from eggs, 11 per cent from dairy products, 10 per cent from oils and margarine, and 6 per cent from cakes.
Living in regions with the highest ultraviolet levels was associated with a significant — nearly 10 per cent — reduced risk compared to those women in the areas with the lowest UV.
But the biggest effects were seen when the researchers examined the impact of both sources of the vitamin. In regions which had the highest level of daily ultraviolet, the women with higher level of vitamin D in their diets or who took supplements had a breast cancer risk 32 to 43 per cent lower compared with those with the lowest vitamin intake.
"Our findings support a protective effect of sun exposure on the risk of breast cancer," says Dr Pierre Engel, who led the study. "It is difficult to have a simple public-health message without thinking about the risk of skin cancer. We must be very cautious but we think that increased vitamin D levels by reasonable sun exposure and higher dietary intakes should be encouraged. Diet alone seems unable to provide an adequate amount of vitamin D."
Eye on intake levels
High dietary and supplemental vitamin D intakes are associated with a reduced risk in women living in areas with higher UV exposure. When a sufficient vitamin D level is secured through UV exposure, variations in dietary intake may become of importance. When the underlying level of vitamin D photosynthesis is low, variations in dietary intake are insufficient to make any difference in disease risk.
"These results confirm other work we have carried out showing that women with high blood vitamin D levels are at reduced risk of breast cancer compared to those who have low levels," Dr Engel says.
In the UK, vitamin D deficiency is a common problem — more than half the population has insufficient levels. Darker skins need more sun to get the same amount of vitamin D as a fair-skinned person. The sunlight required has to fall directly on to exposed skin two to three times a week for up to 30 minutes during summer months (April to September), which should then last throughout the year.
[/img][/COLOR]
