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Various studies have suggested vitamin D supplementation yields certain health benefits. But new research published in The Lancet Diabetes & Endocrinology suggests that evidence to back up these claims is lacking and that future studies are unlikely to change this outlook.
The main source of vitamin D comes from sunlight. However, foods such as oily fish, eggs, fortified fat spreads and powdered milk are good sources of the vitamin. It can also be taken in the form of supplements.
According to the study researchers, led by Dr. Mark Bolland of the University of Auckland in New Zealand, previous studies have linked lack of vitamin D to poor health and early death - research which has helped fuel calls for widespread vitamin D supplementation.
Medical News Today recently reported on a study suggesting that low levels of vitamin D may damage the brain, while other research has linked vitamin D deficiency to increased risk of anemia in children.
Studies have also linked high vitamin D levels with an array of health benefits. A study recently suggested that high vitamin D intake during pregnancy may increase offspring muscle strength, while other research has heralded the vitamin for protecting against heart attack, stroke, bone fractures and cancer.
But the investigators of this most recent analysis say their research suggests that many of the associations found in studies of vitamin D are not causal - meaning there is insufficient evidence to say vitamin D supplementation has any health benefits.
To reach their findings, the research team assessed 40 randomized controlled trials that analyzed the use of vitamin D supplements, with or without calcium supplements.
Their analysis was inconclusive as to whether vitamin D supplementation reduces mortality in the general population by more than 5%.
But the team says their findings suggest that vitamin D supplements, with or without calcium supplements, are unlikely to reduce the incidence of heart attack, heart disease, stroke, cancer and bone fractures.
Commenting on the findings, Dr. Bolland told Medical News Today:
"Lots of observational studies that measure vitamin D levels at baseline and compare health outcomes over time between groups with high levels and low levels have reported associations between low vitamin D levels and poor health outcomes.
These studies are not able to determine causality because of their design. It is possible that low vitamin D levels are simply a marker of ill health, rather than having a causal relationship."
As part of the study, the investigators used a "futility analysis." This is a tool that predicts whether future research may have the potential to influence existing evidence. But they concluded that this would not be the case.
"Trials of vitamin D supplementation in individuals with more pronounced vitamin D deficiency might produce different results," the researchers write.
"However, before such trials are undertaken, there should be strong evidential support underpinning the trial rationale, particularly in view of the absence of effects seen in studies done thus far."
But Dr. Bolland told us that their findings should not encourage people to reduce their vitamin D intake, adding:
"The main message is that if you are otherwise healthy and active, you are likely to receive enough sunshine to have adequate vitamin D levels and don't need to take vitamin D supplements."
He said that future research into vitamin D levels should aim to determine what levels of the vitamin are adequate for good health.
This is not the only research to question the benefits of vitamin D supplementation.
Medical News Today recently reported on a study from researchers at the International Prevention Research Institute in Lyon, France, which cast doubts over the benefits of vitamin D supplements after they found no definitive evidence that they promote health benefits.
This conclusion was reached after they analyzed data from 290 prospective observational studies and 172 randomized trials of vitamin D supplements.
Written by Honor Whiteman
Copyright: Medical News Today
Not to be reproduced without the permission of Medical News Today.
The effect of vitamin D supplementation on skeletal, vascular, or cancer outcomes: a trial sequential meta-analysis, Mark J. Bolland, Andrew Grey, Greg D. Gamble, Ian R. Reid, The Lancet Diabetes & Endocrinology, published 24 January 2014. Abstract
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