Vitamin D appears to be receiving a lot of attention in the scientific and medical press at present with well over 20 studies due for publication in June alone and many, many more already published in 2008.  In fact, as I started to research for this post the current issue of The Proceedings of The Nutrition Society arrived through my letterbox (Volume 67 No.2) and two of the featured papers covered the importance of vitamin D (one in relation to cancer and one in relation to the treatment and prevention of osteoporosis).

Vitamin D is called the sunshine vitamin, though technically vitamin D is a hormone, as it is produced in the body when the skin is exposed to the UVB rays in sunlight.  In theory spending just 10-15 minutes in the sun everyday should supply all the vitamin D that we need.  However, many of us do not get enough sun on our skin to generate adequate amounts of vitamin D especially in the autumn and winter months.  A recent analysis(1) found that there is a global widespread insufficiency of this vital nutrient and there is evidence from the National Diet and Nutrition Surveys (NDNS) which suggests that in the UK vitamin D deficiency is a real problem (2,3,4,5).  The problem is made worse in the older generations since, as we age our bodies find it increasingly difficult to manufacture vitamin D.

This does not make for good news since vitamin D is vital for our health.  Not just the health of our bones and teeth but a for our hearts (the vitamin may protect against atherosclerosis, heart attack and high blood pressure), our digestive systems, the immune system (there is increasing evidence to show that vitamin D is important in the prevention of cancer), blood sugar control (and the prevention of type I and type II diabetes and insulin resistance), muscles, brain (deficiency is linked to depression and mood), fertility and skin health.  Quite a list!

I would like to write a bit more about the link between vitamin D and cancer.  We are constantly told by the media to avoid the sun as it increases our risk of a certain type of skin cancer called ‘malignant melanoma’.  However evidence is now mounting to suggest that insufficient sunlight exposure and low vitamin D levels actually increase the risk of several types of internal cancers such as breast, prostate, colon, bladder, kidney, lung, pancreas and ovary (to name but a few) (6,7).  Just as I was finishing this post a study was published (8) which looked at UVB exposure, vitamin D levels and breast cancer risk across 107 countries.  The authors of the study found that higher blood vitamin D levels were associated with lower rates of breast cancer and UVB exposure had a protective effect on the risk of breast cancer (these effects were independent of potential confounding factors such as fertility rate, overweight, alcohol intake, animal energy intake).  Vitamin D seems to have many cancer protective properties;  it can prevent cells from multiplying and can also specifically induce the death of cancer cells. 

It certainly seems that the sun is very important for our optimal health and wellbeing!

It is essential to be safe in the sun and avoid getting burned and baked, malignant melanoma is a particularly nasty skin cancer.  However , the risk of this type of skin cancer is relatively low in comparison to other forms of cancers and staying out of the sun completely will probably do more harm than good with regard to health and overall cancer risk.  For more interesting information about the benefits of sunlight for health please visit the Sunlight Nutrition And Health Research Centre, the information there is well presented and backed up by significant amounts of good evidence.

The UV in sunlight is believed to be our main source of vitamin D with only small amounts being found in food sources such as oily fish (mackerel, salmon and sardines)and eggs.  Recently, however, there has been mass debate about whether UV exposure in the UK is sufficient to keep vitamin D levels optimal for health.  I mentioned earlier that most of us in the UK are falling short of recommended levels.  If you rarely get out into the sun you may wish to consider a vitamin D supplement which provides around 12mcg/day (around 500iu).  Such a supplement may be particularly useful during the autumn and winter months.

(1) Hagenau T et al.  2008.  Global vitamin D levels in relation to age, gender, skin pigmentation and latitude: an ecologic meta-regression analysis.  Osteoporosis International May [E publication ahead of print]
(2) Finch S et at.  1998.  National Diet and Nutrition Survey of People aged 65 Years and Over.  London: H. M. Sationery Office.
(3) Gregory L et al.  2000.  National Diet and Nutrition Survey of People aged 4-18 years. Vol 1.  Report of the Diet and Nutrition Survey.  London:  The Stationery Office
(4) Henderson L et al.  2002.  National Diet and Nutrition Survey: Adults Aged 19-64 years.  Vol 1: Types and Quantities of Foods Consumed.  London: The Stationery Office
(5) Hypponen E & Power C.  2007.  Hypovitaminosis D in British adults age 45y: nationwide cohort study of dietary and lifestyle predictors.  Am J Clin Nutr.  85:860-888.
(6) Grant WB.  2002.  An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet-B radiation.  Cancer.  94:1867-1875
(7) Grant WB & Garland CF.  2006.  The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates.  Anticancer Research.  26:2687-2699
(8) Mohr SB et al.  2008.  Relationship between low ultraviolet B irradiance and higher breast cancer risk in 107 countries.  Breast J.  14:255-60

Written by Ani Kowal