5 December 2013
Last updated at 20:40 ET
Writing in The Lancet Diabetes and Endocrinology, French researchers suggest low vitamin D levels do not cause ill health, although they did not look at bone diseases.
More clinical trials on non-skeletal diseases are needed, they say.
Vitamin D supplements are recommended for certain groups.
Prof Philippe Autier, from the International Prevention
Research Institute in Lyon, carried out a review of data from 290
prospective observational studies and 172 randomised trials looking at
the effects of vitamin D levels on health outcomes, excluding bone
health, up to December 2012.
'Discrepancy'
Doubt cast on vitamin D's role against disease
Vitamin D supplements are recommended for young children and the elderly
Scientists
have cast doubt on the value of vitamin D supplements to protect
against diseases such as cancers, diabetes and dementia.
More clinical trials on non-skeletal diseases are needed, they say.
Vitamin D supplements are recommended for certain groups.
Continue reading the main story
Prof Philippe Autier International Prevention Research Institute"What this suggests is that decreases in vitamin D levels are a marker of deteriorating health. ”
Recent evidence has shown it may
also have a role to play in preventing non-bone-related diseases such
as Parkinson's, dementia, cancers and inflammatory diseases.
'Discrepancy'
A large number of the observational studies suggested that
there were benefits from high vitamin D - that it could reduce the risk
of cardiovascular events by up to 58%, diabetes by up to 38% and
colorectal cancer by up to 33%.
But the results of the clinical trials found no reduction in risk, even in people with low vitamin D levels.
And a further analysis of recent randomised trials found no positive effect of vitamin D supplements on diseases occurring.
Prof Autier said: "What this discrepancy suggests is that decreases in vitamin D levels are a marker of deteriorating health.
High risk
But the results of the clinical trials found no reduction in risk, even in people with low vitamin D levels.
And a further analysis of recent randomised trials found no positive effect of vitamin D supplements on diseases occurring.
Prof Autier said: "What this discrepancy suggests is that decreases in vitamin D levels are a marker of deteriorating health.
Continue reading the main story
Most people get enough vitamin D by being exposed to the sun for 10 to 15 minutes a day.
A small amount of vitamin D also comes from foods such as oily fish and dairy products.
Recently England's chief medical officer said free vitamins should be given to all young children because more and more of them were being diagnosed with the bone disease rickets, lack of calcium and other bone and muscle diseases.
What is a vitamin D deficiency?
A vitamin D level less than 25nmol/L in the blood is a deficiency, but experts increasingly believe that lower than 60nmol/L can also be damaging to health.Most people get enough vitamin D by being exposed to the sun for 10 to 15 minutes a day.
A small amount of vitamin D also comes from foods such as oily fish and dairy products.
Recently England's chief medical officer said free vitamins should be given to all young children because more and more of them were being diagnosed with the bone disease rickets, lack of calcium and other bone and muscle diseases.
"Ageing and inflammatory
processes involved in disease occurrence... reduce vitamin D
concentrations, which would explain why vitamin D deficiency is reported
in a wide range of disorders."
In the UK, vitamin D supplements are recommended for groups at
higher risk of deficiency, including all pregnant and breastfeeding
women, children under five years old, people aged over 65, and people at
risk of not getting enough exposure to sunlight.
People with dark skin, such as people of African-Caribbean and South Asian origin, and people who wear full-body coverings, as well as pale-skinned people are also known to be at higher risk.
In recent years, there has been a four-fold increase in admissions to UK hospital with rickets - a disease that causes bones to become soft and deformed.
Dr Colin Michie, consultant senior lecturer in paediatrics and chair of the nutrition committee at the Royal College of Paediatrics and Child Health, said the review had little to contribute to the problem in the UK because it excluded the measurement of bone health.
"It has been known for almost a century that vitamin D supplements given to those with deficient vitamin D levels results in improved bone health, preventing hypocalcemic seizure and rickets."
He added that it was important to provide appropriate supplements, such as vitamin D, to improve bone health.
More research
People with dark skin, such as people of African-Caribbean and South Asian origin, and people who wear full-body coverings, as well as pale-skinned people are also known to be at higher risk.
In recent years, there has been a four-fold increase in admissions to UK hospital with rickets - a disease that causes bones to become soft and deformed.
Dr Colin Michie, consultant senior lecturer in paediatrics and chair of the nutrition committee at the Royal College of Paediatrics and Child Health, said the review had little to contribute to the problem in the UK because it excluded the measurement of bone health.
"It has been known for almost a century that vitamin D supplements given to those with deficient vitamin D levels results in improved bone health, preventing hypocalcemic seizure and rickets."
He added that it was important to provide appropriate supplements, such as vitamin D, to improve bone health.
More research
Peter Selby, consultant physician and honorary professor of
metabolic bone disease at Manchester Royal Infirmary, said the French
review was limited.
"It could very well be that the apparent negative results of this study have been obtained simply because they have not been looking at people with sufficient degree of vitamin D insufficiency to have any meaningful biological effect."
But he said the authors were right to say that more interventional research looking at disease outcomes was necessary.
The Scientific Advisory Committee on Nutrition (SACN), an independent group of scientific experts who advise the government on nutrition, is currently reviewing the dietary recommendations for vitamin D for all population groups in the UK.
Their report on vitamin D is expected to go out for public consultation in 2014.
"It could very well be that the apparent negative results of this study have been obtained simply because they have not been looking at people with sufficient degree of vitamin D insufficiency to have any meaningful biological effect."
But he said the authors were right to say that more interventional research looking at disease outcomes was necessary.
The Scientific Advisory Committee on Nutrition (SACN), an independent group of scientific experts who advise the government on nutrition, is currently reviewing the dietary recommendations for vitamin D for all population groups in the UK.
Their report on vitamin D is expected to go out for public consultation in 2014.
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