There is no doubt that a low Vitamin D status is associated with a range of diseases and conditions of ill-health. If it can be confirmed that an inadequate intake of Vitamin D is a contributory factor then it follows that supplementation would have enormous benefits. However there is some debate on the level in the blood that has to be maintained in order to achieve optimum health.

One of the big problems is that there have been few randomised controlled trials (RCTs), which can provide conclusive proof that supplementation is effective. Furthermore it is essential to ensure that the Vitamin D dose is sufficiently high to obtain a substantial increase in the blood concentration as estimated by the content of 25 (OH) Vitamin D.

Vitamin D and cancer

Much progress has been made on this topic by GrassrootsHealth. An investigation reported in 2007 produced very promising results on cancer incidence (1). 1180 women from rural areas in Nebraska were recruited and allocated to one of three different treatments, which consisted of:

  • Controls who took a placebo (n=288);
  • A supplement of calcium (n=445);
  • A supplement of calcium plus Vitamin D (1,100 IU of Vitamin D3/day)(n=446).

The study continued for 4 years, when the information was collated for the incidence of all cancers. Excluding those who developed cancer during the first year, to eliminate any that might have been initiated before the start of the trial, it was found that in the calcium plus Vitamin D group, the cancer rate was reduced by over 75%, compared with the controls. In this group the blood levels of Vitamin D increased from 71.1 nmol/L at the outset to 96.0 nmol/L after 12 months but it was unchanged in the other groups. It was estimated an increase of 25 nmol/L would reduce the risk of cancer development by 35%.

The monitoring of this group of women was maintained after the completion of the above project in order to compare them with another cohort of Volunteers in the GrassrootsHealth programme (GRH) (3). This consisted of 1,135 women who were recruited to match those in the Nebraska-based study. However they were taking Vitamin D supplements and so their Vitamin D status would have been much higher than in the other group. The information obtained enabled the researchers to compare the incidence of cancer over a wide range of values for the concentration of 25(OH)D (a measure of the Vitamin D concentration) in the blood. It was found that if the concentration was >100 nmol/L the risk of cancer was reduced by 67% compared with those with a concentration of <50 nmol/L.

Vitamin D and Alzheimer’s Disease (AD)

In a similar study, 1,658 adults, who were free of dementia, cardiovascular disease and stroke at the beginning, were followed for 5.6 years (3).

171 participants developed all-cause dementia and 102 developed AD. It was found that those with blood 25(OH)D of <25 nmol/L had more than twice the incidence of dementia and AD compared with those whose values were >50 nmol/L.

Once again these results are consistent with the hypothesis that insufficient Vitamin D is a critical factor in the development of a serious chronic disease.

Vitamin D and type 2 diabetes (T2D)

In this study, a comparison was made between the GRH and data obtained from the US National Health and Nutrition Examination Survey (NHANES) (4). When adjustments were made for differences in characteristics of the 2 groups, it was found that the incidence of T2D in the NHANES group was three times that of the GRH. The 25(OH)D concentration was 102 nmol/L in the GRH but only 55 nmol/L in the NHANES. Obviously this is not conclusive proof that increasing the intake of Vitamin D would reduce the incidence of T2D but it is one more piece of evidence that fits the picture.

Vitamin D and Multiple Sclerosis (MS)

There is good evidence that a low blood level of 25(OH)D is one of the important risk factors for MS. It has certainly been established by epidemiological studies that exposure to sunshine can make a big difference to the incidence. Professor George Ebers of Oxford University has noted that if people move from the UK to Australia the risk is substantially reduced (5). Within Australia, there is a much higher rate in Tasmania than in Queensland, which is sub-tropical and therefore has lots more sunshine. He has also found that the incidence of MS is much lower in Norway than in Scotland, even though the exposure to sunshine is roughly the same. He believes this is because the Norwegians have a high intake of fish contains high quantities of Vitamin D. He is a strong advocate of supplementation, although there is still not possible to guarantee that this will be successful. His view is:

“When looking at the risks, costs and benefit equation, the risks seem tiny, and the benefits are yet to be established but indirect studies are supportive. The cost of vitamin D is dirt cheap but the costs of MS are staggering and are increasing.”

He contends that the vast majority of us don’t spend much time in sunshine. This means we are Vitamin D deficient and therefore supplementation makes sense. With respect to toxicity and specifically that supplementation may cause renal failure he has no concerns. He says the margin of safety is greater than for water and that there is no problem with taking 4,000 IU/day.


On the basis, of the accumulated evidence there is a strong case for taking supplements up to about 4,000 IU /day as Professor Ebers advocates. Bear in mind that his main interest is MS and when all the other factors are taken into consideration this would seem to be sound advice. There is little doubt that the recommendation by the Scientific Advisory Committee on Nutrition in the UK is far too cautious (6).  It suggests a that blood level of >25nmol/day is sufficient and that the recommended intake should be 400 IU/day, which is only 10% of the figure advocated by professor Ebers. All the indications are that it should be at least double that value and possibly even higher. GrassrootsHealth propose that the blood level should be >100nmol/L.


  1. J M Lappe et al (2007).
  2. S L McDonnell et al (2016).
  3. T J Littlejohns (2014).
  4. S L McDonnell et al (2014).