In Blog 48 I explained how the brothers Cedric and Frank Garland identified the possible link between exposure to sunshine, which resulted in the formation of Vitamin D in the skin, and the incidence of colon cancer. Since then there have been many studies that confirm these ideas.

William Grant conducted an ecological study of cancer mortality rates in different areas of the USA with respect to exposure of solar UV-B (1). He found that the mortality rates are correlated with the solar exposure for 13 cancers. For men these are cancer of the bladder, colon, oesophagus, , prostate, rectum, stomach and  non-Hodgkin lymphoma. For women these are cancer of the bladder, breast, colon, kidney, ovary, rectum, stomach, uterus and non-Hodgkin lymphoma. On the basis of these results he estimated that about 15,000 white and 700 black Americans died prematurely from cancer every year between 1970 and 1994 due to insufficient exposure to solar UV-B.

Data collected from 47,800 men who participated in the Health Professionals’ Follow-Up Study were used to relate the level of serum 25(OH)Vitamin D to the incidence of cancer. Between 1986 and 2000 there were 4286 cases of cancer diagnosed (excluding organ-confined prostate cancer and non-melanoma skin cancer).Of these 2025 resulted in death. It was found that an increment of 25 nmol/L in the predicted level of the 25(OH)Vitamin D was associated with a reduction of 29% in the death rate for all cancers but for cancers of the digestive system(colorectal, pancreatic and oesophageal cancers) the reduction was 45%. The authors noted that there are 295,000 deaths from cancer in men in the USA every year and that a reduction in 29% would be equivalent to 85,550 fewer deaths. In order to increase the level of vitamin D in the body the most effective means is exposure to sunlight. The degree of exposure required can be achieved without risk of developing skin cancer. Even if the necessary precautions are not taken to avoid skin cancer the total annual number of deaths in men is about 7,000, which is considerably lower than those likely to be saved if the vitamin D level is raised(2,3).

In Norway a study based on 115,096 cases and 45,667 deaths due to breast, colon or prostate cancer between 1964 and 1992 found that the death rate for those diagnosed in the summer and autumn, when vitamin D levels would be relatively high was about 30% lower than those diagnosed in the winter when the levels would be much lower. It is important to note that there was no seasonal variation in the number of diagnosed cases for any of the cancers. This suggests that raised level of vitamin D at the time of diagnosis and possibly also during treatment may improve the prognosis of these particular types of cancer (4).

While these investigations suggest that many people would benefit from supplementation with Vitamin D the only way to confirm that is the case is to conduct an experiment. Joan Lappe and colleagues at Creighton University in Nebraska have done just this(5). A total of 1179 post-menopausal women aged over 55 years were selected for participation in a double-blind randomized trial, which lasted for 4 years. There were 3 different treatments:

  • Placebo
  • 1500 mg calcium/day
  • Calcium plus 1100 International Units(IU)/day

Almost 87% of the participants completed the study which is an excellent result.

When any cancers diagnosed in the first year were excluded (to eliminate any which might have been initiated before the study commenced) it was found that those who were taking Vitamin D plus calcium had a relative risk of death due to cancer which was 0.23. In other words their risk of cancer was just one quarter that of those taking the placebo. Those taking calcium only had the same risk as those on the placebo. This reduction in the risk of developing cancer is absolutely huge! It is certainly much greater than could be achieved by the use of drugs. It is especially significant that it fits in with and provides support for the epidemiological results. In this investigation it is not possible to be definitive about the role of the calcium as there was no treatment which was confined to Vitamin D on its own. It is also worth noting that some researchers advocate an even higher dose than 1100IU/day so it is possible that even more favourable results can be achieved.

The importance of the dose is illustrated by results from the Women’s Health Initiative which concluded that Vitamin D supplementation did not cause any reduction in the incidence of colon cancer. In this study the women were given either a placebo or 1000 mg calcium plus 400IU Vitamin D/day. However the dose of 400IU per day was insufficient to increase the Vitamin D in the blood to an optimal level. In addition the compliance was only about 50% (6).

Although I have only referred to a limited number of studies, the evidence which emerges is extremely convincing. Essentially there are many people with blood levels of Vitamin D that are inadequate because there is insufficient in their diet and they lack exposure to enough sunlight to generate their own. There can be little doubt that everyone should ensure they have optimal levels of Vitamin D in their body. In the British Isles this is probably best achieved by getting out into the sun (when it shines!) and taking supplements the rest of the time. It is highly unlikely that this can be achieved by diet alone. In fact is rather ironic that as Vitamin D is fat soluble those who are actively reducing their fat intake are probably limiting even more the amount supplied by their food.


  1. W B Grant(2002) Cancer 94 (6) pp 1867-1875
  2. E Giovannucci (2005) Cancer Causes and Control 16 (2) pp 83-95
  3. E Giovannucci et al (2006) Journal of National Cancer Institute 98 (7)pp 451-459
  4. T E Robsahm et al (2004) Cancer Causes and Control 15 (2) pp149-58
  5. J M Lappe et al American Journal of Clinical Nutrition 85 (6) pp 1586-1591
  6. W J Wactawski et al (2006) 354 (7) pp 684-696