A comprehensive review in the Lancet Diabetes & Endocrinology found low vitamin D levels are not a cause but a consequence of ill health, raising doubt over whether vitamin D supplements protect against serious disease.
Catherine Collins, Principal Dietitian at St George’s Hospital NHS Trust, St George’s Healthcare NHS Trust, said:
“What should we take from this? Vitamin D intake remains a cause for concern amongst UK Registered Dietitians, and our advice would be to continue to ensure an intake of at least 10 mcg (800IU) daily, especially if you avoid the sun, are pregnant, housebound, or cover up outdoors. We also recommend that young children take vitamin D supplements as recommended by the Chief Medical Officer.
“Difficulties of nutrition research are highlighted in this study ranging from the type of supplement used, to whether blood levels were accurately measured, and whether you could expect to see a difference in disease risk over a short time period of a couple of years. Whilst interesting, there’s no reason to change our recommendations that we should continue considering the importance of vitamin D from food, supplements or sun for all age groups. Vitamin D is absolutely essential for bone health, and this comprehensive paper doesn’t really allow us to ignore its potential for other conditions as well.
“The authors confirm that heart disease, high blood pressure, stroke and colorectal cancer incidence seem reduced with higher blood levels of vitamin D. This may reflect healthy diet and lifestyle such as outdoor exercise, oily fish intake, supplements and obesity – all of which influence your blood levels of vitamin D. Have the authors proved that taking supplements doesn’t give health protection? I’d suggest it’s tentative evidence but with so many holes in the argument it’s hard to accept without reservation. They did show that in a lot of the studies a good rise in blood vitamin D level wasn’t achieved, so their outcomes suggest non-compliance or a blood level quite similar to the ‘control’ or test group.”
Dr Nigel Belshaw, Research Leader, Institute of Food Research, said:
“This paper is very useful because it highlights the need for more long term intervention studies specifically looking at the effect of proper vitamin D supplementation on disease risk. When we look at vitamin D levels in the population we find that low vitamin D status is associated with an increased risk of disease, but currently we can’t tell whether low vitamin D levels themselves promote disease, or if the diseased state indirectly lowers vitamin D levels in the blood.
“However, it does not suggest that taking vitamin D supplements cannot be useful in some cases for some purposes. Neither does it rule out a health advantage of increasing vitamin D levels in the blood for those who are deficient.
“There are other benefits of maintaining a healthy vitamin D status, which may be achievable through supplementation. Increasing your vitamin D level may still confer additional advantages: vitamin D is essential for bone health, orchestrating absorption of calcium in the gut and maintaining bone density into later life (which reduces the risk of osteoporosis).”
Professor David Thurnham, Emeritus Professor of Human Nutrition, University of Ulster, said:
“This review paper reports that there is a discrepancy between observational studies and intervention studies looking at vitamin D, and suggests that a low plasma vitamin D level is a marker, rather than a cause, of ill health. This conclusion should not surprise us – previous studies have shown vitamin D levels fell significantly in individuals following surgery, and that the fall in vitamin D was associated with a rise in level of an inflammatory biomarker. Indeed it has previously been shown that inflammation in the body is associated with falls in levels of various vitamins and nutrients, including vitamin A, beta-carotene, iron, zinc and vitamin B6.
“We don’t always know the reason for the falls in levels of these micronutrients, but the reductions are physiological processes and might act to benefit the host. Therefore, supplementation in response to falling levels due to chronic or acute disease may not always be beneficial. We will all remember that smokers had low levels of beta-carotene but giving supplements increased mortality from lung cancer.
“Should we take vitamin D supplements for other reasons? Vitamin D is important for bone health. We obtain most of our vitamin D from sunlight but only during the summer months. Most young people obtain sufficient vitamin D to accumulated stores to cover their needs for both the summer and winter months. However, elderly people may not be able to take full advantage of summer sunshine; they may be too frail to venture outside during peak sunlight hours and the skin loses some ability to synthesize vitamin D as we age, so many elderly people may be at risk of vitamin D deficiency in this country particularly during the winter months and may benefit from taking supplements. People who cover their skin for cultural reasons are also at risk of vitamin D deficiency and should take supplements. A supplement containing 10 micrograms per day is sufficient (RDA, recommended daily allowance).
“Why did we think that vitamin D might have a role in disease prevention? The classical role of vitamin D was to provide for healthy bone development. However, studies demonstrated that the receptors for metabolically active vitamin D were not just present on cartilage tissue but also on the surface of many cells with immunological properties. This observation gave birth to the idea that vitamin D could have a role in preventing disease and subsequent work has shown that vitamin D is a component of our immune response, but research has not yet shown for sure what part vitamin D plays.
“Where else do we get vitamin D from? Dietary sources of vitamin D include dairy products, eggs and fish (especially the liver). Dietary sources do not provide the amount needed for the recommended daily allowance, so some sunlight exposure is necessary.”
Professor Helen Macdonald, Professor of Nutrition and Musculoskeletal Health, University of Aberdeen, and Nutritional Advisor, National Osteoporosis Society, said:
“Vitamin D is important for bone health and we already know that people who are at risk of vitamin D deficiency, like older people, pregnant and breastfeeding women, young children and people with darker skin, need to take a supplement because it is difficult to boost vitamin D levels from food sources alone. This meta-analysis also confirms what we have suspected for a while – that healthy people probably don’t need to take a high dose supplement and that the best source of vitamin D for most people is sunlight in the summer, always taking care not to burn.”
Professor Cyrus Cooper, Director, and Professor of Rheumatology, Medical Research Council Lifecourse Epidemiology Unit, University of Southampton, said:
“This paper usefully documents the disparities within the evidence base relating to vitamin D supplementation, with findings in accord with those from our own work. We echo the call for high-quality intervention studies to definitively answer questions posed by the observational epidemiology, and indeed are nearing completion of a large multicentre randomised controlled trial of vitamin D supplementation in pregnancy, aimed at optimising offspring bone mass and body composition. Only with such rigorous investigative approaches will we be able to clarify the place of vitamin D supplementation in human health.”
Dr Nicholas Harvey, Senior Lecturer and Honorary Consultant Rheumatologist, Medical Research Council Lifecourse Epidemiology Unit, University of Southampton, said:
“We are in complete agreement with the need to test, through randomised controlled trials, observational findings relating to vitamin D supplementation. Indeed, in our systematic review of vitamin D supplementation in pregnancy, currently in press, we identified potential benefits for offspring birth weight, bone mass and calcium concentrations, but the lack of high quality intervention studies clearly limited the potential for any definitive clinical recommendations to be made. Although in most disease areas the benefit, or lack of benefit, of vitamin D supplementation remains uncertain, several large high-quality trials, currently ongoing, including our own trial of vitamin D supplementation in pregnancy, should provide more definite answers over the coming years.”
Professor Peter Selby, Consultant Physician and Honorary Clinical Professor of Metabolic Bone Disease, Manchester Royal Infirmary, said:
“One problem with this sort of systematic review is that it can only examine the studies which have been published previously, so it is limited by the level of vitamin D in subjects in these studies. Their choice of a level of 75 nmol per litre to define vitamin D sufficiency flies against the recent recommendations in this country and the USA, which suggest that for the majority of people levels of 40 nmol per litre may well be satisfactory. 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.
“The authors make a good point in the review that more interventional research looking at disease outcomes is necessary.
“It is important not to let the apparently negative finding of the study take anything away from the importance of adequate vitamin D nutrition in the management of bone disease. Recent guidelines relating to vitamin D deficiency were published by the National Osteoporosis Society together with several other professional organisations; these provide widely accepted guidance for the diagnosis and treatment of vitamin D deficiency (http://www.nos.org.uk/document.doc?id=1352).”
Dr Colin Michie, Consultant Senior Lecturer in Paediatrics, Ealing Hospital NHS Trust, and Chair of the Nutrition Committee, Royal College of Paediatrics and Child Health, said:
“From the perspective of a paediatrician, this paper is a valuable contribution in the field of nutrition, but it has little to contribute to our problem in the UK, where low levels of vitamin D result in hypocalcemic seizures in infants and bony disorders such as rickets. The studies described have been selected so as to exclude those measuring 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.
“The suggestion that vitamin D levels are low because of co-morbidity is not surprising or novel. This has been proposed in many clinical situations in paediatrics. However it leads to the obvious corollary that such co-morbidities, by reducing vitamin D levels, may compromise skeletal health. From the patient’s perspective it therefore becomes important to ensure this does not happen by providing appropriate supplements, including vitamin D. This is a rather circular argument and one that has not been well researched.”
Dr Benjamin Jacobs, Consultant Paediatrician and Director of Children’s Service, Royal National Orthopaedic Hospital, said:
“The problems of Vitamin D deficiency had been thought to be solved in the 1950s but this paper shows there is still much to be learned. A hundred years ago rickets was a major problem in the UK. Then in the 1950s it was thought that Vitamin D deficiency was solved, which is why we do not fortify foods or give babies Vitamin supplements as much as most of Europe and North America.
“But now we are seeing many children again with rickets, lack of calcium and other bone and muscle diseases. England’s Chief Medical Officer recently announced her intention to remedy this deficiency, and the publication of this paper today shows the need for better research to evaluate the role of Vitamin D in many diseases. We do not have enough data and may have to wait another 5 years before making recommendations for the whole UK population. Meanwhile we must continue the current guidance: All pregnant and breastfeeding mothers in this country should take a daily vitamin D supplement, and so should all children from the age of 6 months to 5 years.”
‘Vitamin D status and ill health: a systematic review’ by Philippe Autier et al. published in Lancet Diabetes & Endocrinology on Friday 6 December 2013.