The ‘umbrella’ review of vitamin D studies that found a myriad of health links for the sunshine vitamin were unconfirmed in the scientific literature, has been criticised for containing too many flawed studies that warped the overall findings.
The British Medical Journal (BMJ) findings have been called “irresponsible” and contrary to public health guidelines, not to mention approved health claims for the vitamin in many parts of the world including about 10 approved claims under the EU’s tough nutrition and health claims regulation (NHCR).
Leading researcher, Dr Heike Bischoff-Ferrari, from the Department of Geriatrics and Aging Research at the University of Zurich said the findings were, “un-nuanced”.
“…we question if we get better answers from meta-analyses of meta-analyses without addressing what has repeatedly been demonstrated before - that conclusions drawn from meta-analyses of vitamin D trials vary greatly as a function of the trials included, adherence and dose.”
“A significant benefit of vitamin D supplementation has been demonstrated in meta-analyses from double-blind, randomised controlled trials and a median dose of 800 IU for both falls and fractures – which is consistent with current recommendations of vitamin D.”
The UK Health Food Manufacturers’ Association (HFMA) has said the findings fly in the face of public health recommendations in the UK and elsewhere.
Flawed studies, flawed analysis…
Australian nutritionist, Simon Spedding, said flawed studies had seriously flawed the findings, and he noted John Ioannidis, one of the authors of the umbrella review, had acknowledged its limitations in this way.
“Which way up was the umbrella? Did this review collect knowledge or shield us from it?” Spedding asked.
“Author John Ioannidis described umbrella reviews as, ‘subjective and suboptimal’, ‘limited by the data in the primary studies’, and the process of ‘patching together pre-existing reviews’, thus open to subjective interpretations based on the authors opinions.”
“The question remains why did these authors not present a review of flawed and unflawed studies in a review claimed to be all-encompassing?”
Dr Manfred Eggersdorfer, senior vice president in nutrition science and advocacy at the world’s biggest vitamins supplier, DSM Nutritional Products, agreed that the umbrella review was never going to find strong associations when so many underpowered and poorly designed trails were in the mix.
“This is irresponsible and gives the wrong message to the public,” said Dr Eggersdorfer. “The quality of the trials must be taken into account.”
He noted many large scale vitamin D trials were underway and could strengthen the overall body of vitamin D work.
In the study published in the BMJ last week the researchers concluded, “universal conclusions about its [vitamin D’s] benefits cannot be drawn.”
The authors themselves acknowledged flaws such as:
- Low doses
- Large differences in baseline plasma concentrations of 25-hydroxyvitamin D
- Contamination with private use of vitamin D
Dr Carrie Ruxton, nutritionist and spokesperson for the Health Supplements Information Service (HSIS) said vitamin D deficiency remained a major problem in Europe and other parts of the world.
“ In the UK, for example, more than one in five adults and teenagers are vitamin D deficient, according to accepted minimum cut-offs for bone health (<25 nmol/L 25-hydroxyvitamin D),” she said. [The BMJ recommended doctors cease using the <25 nmol/L 25-hydroxyvitamin D measure]
She added: “The European Food Safety Authority (EFSA), not the easiest organisation to convince, has confirmed the essential role of vitamin D in normal bone health and immune function.”
“Now, if some researchers persist in claiming that vitamin D has no positive effect on health, we are risking public apathy about ensuring a good vitamin D status for all. A more responsible position is to highlight the importance of vitamin D to bone health and immune function, acknowledge that more research is needed for other chronic conditions, and advise the public on the best ways to improve vitamin D status.”
“These are safe regular sun exposure during summer, weekly oily fish consumption, daily vitamin D supplements especially during Winter, and fortified foods.”
Dr Robert Verkerk, the executive and scientific director at the Alliance for Natural Health International (ANh-I), said the case highlighted broader issues in nutrition science.
“[They] appear to be in search of a magic bullet that will never be found,” said Dr Verkerk of views expressed in a BMJ editorial .
“While they suggest that bias may at least partially explain the trials that have shown benefits, they fail to consider that there might be something fundamentally wrong with using a randomised controlled trial approach with a single intervention, vitamin D in this case.”
“This vitamin has a complex, hormonal mode of action and functions as part of a much more bigger system and there are huge variables that affect responses among different individuals. The danger of continuing to proceed with this approach — and doing nothing until definitive evidence of causal proof is established from intervention trials – is that little will emerge from the pipeline because it’s plugged into the wrong scientific method.”
“Let’s look forward to the day when multi-factorial studies are conducted within a comparative effectiveness research (CER) framework.”
“nutrient of public health significance”
In the US,the Council for Responsible Nutrition (CRN), said the data contained hard-to-explain anomalies but backed ongoing supplementation.
“As we’ve seen in other studies, there is something about certain diseases that seems to either be depleting the body of normal levels of vitamin D, or the low levels are contributing to the disease,” said Duffy MacKay, senior vice president, scientific and regulatory affairs at CRN.
“In either case, where patients present with insufficient levels of this critical nutrient, supplementing with vitamin D makes sense—whether it actually slows the progression of the disease or rather helps to replace the depleted nutrient levels being caused by the disease.”
The US Institute of Medicine recently raised the recommended levels for vitamin D and the US Food and Drug Administration (FDA) recognises it as a, “nutrient of public health significance”.