By Ross Walker

Vitamin D is a fat soluble vitamin that has an important place in calcium metabolism, steroid and cholesterol production. There are three possible sources of vitamin D which include sunlight, certain foods such as oily fish, fish and beef liver, egg yolks and certain fortified foods. The final source of vitamin D is supplementation. It is estimated that somewhere between 30 to 40% of adults are deficient in vitamin D. The definition of vitamin D deficiency is a blood level less than 50 nmol per litre.

Is the deficiency being overestimated?

A recent editorial in the New England Journal of Medicine, however, has raised concerns that the degree of vitamin D deficiency is being widely overestimated. A flow on effect of this alleged overestimation is excessive blood testing for vitamin D levels. The costs to governments has skyrocketed over the last decade, with vitamin D assessments being said to be the fifth most common test measured. The authors of this editorial are suggesting that the cut-off point of 50 nmol per litre is an overestimation of deficiency and for the vast majority of people less than 70, 600 international units daily from any of the sources mentioned, and 800 international units daily for people over 70, is adequate intake.

The bottom line

The bottom line from their interpretation of the studies is that, in reality, only 6% people living in the US up to age 70 are deficient, and we’re not really living in the epidemic of vitamin D deficiency. I must say, this is in contradiction to many studies that have been performed over the past decade, and just because it has been written up in the New England Journal of Medicine does not make it gospel truth. Interestingly, many conservative researchers are only focusing on the link between low vitamin D and osteoporosis, tending to ignore the other significant associations. There have been a number of research studies suggesting a link between low vitamin D levels and cardiovascular disease, cancer, multiple sclerosis, Type II diabetes and depression.

The benefits of normal vitamin D levels

Two recent reports have highlighted the potential benefits of maintaining normal vitamin D levels. In Australia alone, around 15,000 women are diagnosed each year with breast cancer with just under 3000 deaths per year from the disease. There is mixed information around the benefits of vitamin D as an adjunctive therapy for cancer, with strong evidence in animal experimentation that the active version of vitamin D known as calcitriol can reduce the proliferation and growth of cancer cells, decrease cancer blood vessel formation, and stimulate cancer cell death. There is not enough human data as yet to strongly support the use of vitamin D supplements as a way of preventing and treating cancer, but, some of the preliminary work is certainly suggestive. 

The studies

A new study from New York looked that just under 1670 women who were diagnosed with breast cancer. These women were part of the Pathways Study and followed regularly for an eight-year period. The average age was 59 years, and half were said to be vitamin D deficient. The lowest levels of vitamin D were found in women with advanced tumours and especially in premenopausal women with triple negative breast cancer. Levels of vitamin D were inversely proportional to disease progression and death rates. This was a purely observational trial, where vitamin D therapy was not actually used. It is not known whether the advanced nature of some women’s disease actually dropped the vitamin D levels or whether the low levels of vitamin D predisposed them to the disease in the first place. A proper placebo controlled trial needs to be implemented.  

Another recent trial presented at the Society for Endocrinology conference in Britain looked at the association between low vitamin D levels and bladder cancer. The group, from the UK, carried out a systematic review of seven studies to determine this link. The number of participants ranged from between 112 up to 1125. Five out of seven studies found a higher rate of bladder cancer with low vitamin D levels. High vitamin D levels also correlated with better survival outcomes in these groups. The researchers also looked at the cells that line the bladder known as transitional epithelial cells. The cells responded to vitamin D and vitamin D affected the local immune response recognising abnormal cells and preventing cancer formation. 

Although we do not have any large, well-controlled randomised trials of vitamin D for the number of the conditions I have mentioned above, it is my opinion that the evidence is so compelling that taking 1000 international units of D3 on a daily basis is harmless, and almost never puts the vitamin D into potentially toxic ranges, and it is certainly something I do on a daily basis for all of the above reasons.