Previously, I have written about the health benefits of sunlight, and in particular the role of vitamin D in promoting and preserving the wellbeing of both body and brain. For instance, in recent times I have highlighted research which links vitamin D with relative protection from cardiovascular disease, improved physical function in the elderly (here and here), and reduced risk of multiple sclerosis. Vitamin D also seems to have the capacity to quell cancer risk too. See here and here for more on this.
Recently, some scientists based in the USA wrote a review of the potential for vitamin D to combat cancer of the breast and colon. The review, which appeared in the journal Nutrition Reviews, assessed evidence from a total of 29 individual studies [1]. Because it’s not yet available on-line, I’ve not had sight of this study yet. However, if the reports of the study I’ve read are true, this research appears to provide quite a strong argument for us bumping up our blood levels of vitamin D.
Apparently, this research reveals, as expected, that for higher levels of vitamin D in the body were associated with a reduced risk of both colon and breast cancer. Significant protection appeared to ‘kick in’ at vitamin D levels of 22 ng/mL (nanograms per millilitre of blood) for colon cancer and 32 ng/mL for cancer of the breast. The authors of this study calculate that if Americans were to maintain a vitamin D level of at least 55 ng/mL, annual deaths due to colon and breast cancer would fall by 60,000 and 85,000 respectively. They also draw attention to the fact that the average vitamin D levels in Americans in the late-winter (when vitamin D levels are generally at their lowest in the year) are a mere 15-18 ng/mL.
The authors of the study suggest that adults should supplement with vitamin D at a dose of 2000 IU (international units) a day. They specifically recommend that this should come in the form of vitamin D3: this form of vitamin D (also known as cholecalciferol) is believed to be more potent than the other main form of vitamin D known as D2 (also known as ergocalciferol).
This level of vitamin D (2000 IU) intake is often advised as the ‘tolerable upper intake level’. However, there has been a recent call for this upper to limited to be raised five-fold to 10,000 IU [2].
Cedric Garland, the lead author of this study and cancer prevention specialist at the University of California in San Diego, recommends that optimal vitamin D levels might be achieved not just through diet (e.g. oily fish) and supplementation, but through, of course, sunlight exposure. He points our attention to the fact that useful amounts of vitamin D can be made in the midday sun quite quickly. Apparently, a white-skinned individual would only need to expose 40 per cent of their skin for 3 minutes to get benefit. For a given sun strength, dark-skinned individuals need more time to get the same amount of vitamin D. 15 minutes is recommended for such individuals. As sunscreens can block vitamin D production, this sun exposure needs to be without such protection.
Cedric Garland’s study is interesting in that it again highlights the value of vitamin D. It also, I think, questions whether we have got our recommendations regarding vitamin D intake right. And finally, it suggests that even relatively short bursts of sunshine, not enough to burn the skin, may help maintain vitamin D levels and ward off a range of conditions including cancer.
References:
1. Garland C, et al. Nutrition Reviews 2007;65:S91-S95
2. Hathcock JN, et al. Risk assessment for vitamin D. American Journal of Clinical Nutrition 2007;85(1):6-18
