“We need a balanced view on vitamin D, with not too little and not too much. Because clear evidence of benefit over harm for vitamin D has not been proved, we should not recommend vitamin D supplements for prevention of chronic diseases (such as cardiovascular disease, cancer, chronic obstructive lung disease, or diabetes) until more definitive further research evidence is available,” the researchers wrote in the British Medical Journal.
The researchers from the Norwegian Institute of Public Health, the University of Oslo in Norway and the Netherland’s VU University Medical Centre said previous findings had made vitamin D deficiency tests and the recommendation of vitamin D supplements a common health-worker strategy, with some doses far exceeding daily allowances and dietary reference values despite “limited evidence” of a beneficial effect.
“The likely costs of large scale high dose supplementation and concomitant monitoring would first need to be justified by evidence of benefit.”
However, the systematic review did conclude that supplementation of 15-20 micrograms (600-800 international units) of vitamin D per day in combination with calcium (0-1000 mg/day depending on dairy intake) could be recommended to prevent fractures in elderly people.
Shouldn’t be ignored, but shouldn’t always be tested
Professor Haakon Meyer of the Norwegian Institute of Public Health said these conclusions did not mean vitamin D deficiency should be ignored.
According to the Norwegian Directorate of Health, 10 micrograms (µg) of vitamin D per day is recommended for adults and children and 20 µg for the elderly.
However, Meyer said: “A blood test is not needed to follow these recommendations. In the summer months, sufficient exposure to sunlight will help many to achieve these levels regardless of diet. In winter, many people need to take a supplement, such as cod liver oil.”
Recommendations for further research:
- Population: People over 60 years with low vitamin D status (serum 25-hydroxyvitamin D3 less than 50 nmol/L)
- Intervention: Vitamin D3 800 IU/day or vitamin D3 2000 IU/day.
- Control: Placebo
- Outcome: Cardiovascular disease, type 2 diabetes, respiratory diseases, cancer, mortality
The researchers said given all the uncertainties in observational data, it made sense to limit measurement of vitamin D in the blood to situations where it was unclear whether or not to supplement.
On the risks of ‘overdosing’ on vitamin D, they said the risks of toxicity were low, but side effects from high doses could not be excluded. Past research had suggested combined calcium and vitamin D supplementation increased the risk of developing kidney stones (nephrolithiasis).
Ongoing large-scale trials on vitamin D and chronic disease prevention could shed further light on the topic, they wrote, with these results expected to be published within the next five years.
Source: British Medical Journal
Published January 29. doi: http://dx.doi.org/10.1136/bmj.h321
“Should vitamin D supplements be recommended to prevent chronic diseases?”
Authors: H. E. Meyer, K. Holvik and P. Lips