It is good for your bones, it wards off rickets in children, but spending money on vitamin D supplements to prevent cancer and other non-skeletal diseases could be a waste of money, the medical journal The Lancet says.
The finding is the latest attack on the very healthy and growing supplement industry, estimated to generate $1.5 billion in Australian sales a year.
Only last month the US journal Annals of Internal Medicine said most vitamins and mineral supplements didn't prevent chronic disease or death, their use among healthy adults was not justified, they waste money and they should be avoided.
While evidence supports the importance of vitamin D for bone health, Lancet's January editorial said the results of myriad controlled trials were ''almost unanimous'' in concluding that vitamin D supplementation provided protection from few, if any, other diseases.
''It looks increasingly likely that low vitamin D is not a cause but a consequence of ill health,'' said the January editorial in The Lancet Diabetes & Endocrinology medical journal.
Vitamin D, the sunshine vitamin, has been touted as providing protection against cancer, heart attack, diabetes, dementia and auto-immune and inflammatory diseases.
But the French review of nearly 500 studies - which appeared in The Lancet - found its benefits in reducing the risk of diseases as shown in 290 observational studies were largely unconfirmed in 172 randomised controlled trials.
''Associations between vitamin D and health disorders reported by investigators of observational studies are not causal,'' said the report's lead author, Philippe Autier. ''Low vitamin D could be the result of inflammatory processes involved in the occurrence and progression of disease.''
Around 70 per cent of Australians take some form of vitamin or mineral supplement, many of which include D3. It is estimated that around 50 per cent of Americans, 30 per cent of Britons and many Australians take stand-alone vitamin D supplements. Screening for vitamin D deficiency, which can cause tiredness, lethargy and other symptoms, has grown so much that the Royal College of Pathologists of Australasia estimated that at least half the 4 million tests taken each year should not have been done.
The pathologists recommend testing and supplements only for people with conditions such as osteoporosis or chronic kidney failure that are known to decrease vitamin D or for risk groups such as people with dark skin.