French researchers analyzed data from 290 prospective observational studies, and found that high blood levels of the sunshine vitamin might be protective. Indeed, the observational data indicated that high vitamin D levels were associated with a reduction in the risk of cardiovascular events of up to 58%, a reduction in the risk of diabetes of up to 38%, a reduction in the risk of colorectal cancer of up to 33%, and a reduction in the risk of so-called ‘all-cause mortality’ of up to 29%.
High vitamin D levels were also associated with improvements in cholesterol levels, markers of inflammation, glucose metabolism disorders, infectious diseases, weight gain, and cognitive function.
On the other hand, the overall data from 172 randomized clinical trials of vitamin D and non-bone health outcomes indicated no reduction in risk, leading the researchers to conclude that that low vitamin D is not a cause but a consequence of ill health
Professor Philippe Autier from the International Prevention Research Institute in Lyon, France and lead author on the review, said: “What this discrepancy suggests is that decreases in vitamin D levels are a marker of deteriorating health. Aging and inflammatory processes involved in disease occurrence and clinical course reduce vitamin D concentrations, which would explain why vitamin D deficiency is reported in a wide range of disorders.
“If the health benefits of high vitamin D concentrations shown by data from observational studies are not reproduced in randomized trials (the gold standard method for assessing a causal relation between an exposure and an outcome) then the relation between vitamin D status and disorders are probably the result of confounding or physiological events involved in these disorders.”
‘Essential’
Vitamin D facts
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol.
Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
Vitamin D deficiency (less than 20 ng/mL) can cause a number of health issues, including rickets and other musculoskeletal diseases.
Cara Welch, PhD, Sr Vice President, Scientific & Regulatory Affairs for the Natural Products Association (NPA), told us that: "We’re looking at a mother of all meta-analyses, but just on non-skeletal disorders because, as the authors state, they are looking outside vitamin D’s proven “importance in bone health and calcium homeostasis.” So on the non-skeletal disorders, this study seems to confirm what the industry already acknowledges – vitamin D is not the magic pill for all diseases.
"However, I think it also corroborates what we’ve been saying about proper supplementation. There are populations that would benefit from supplementation, people who are prone to vitamin D deficiency and aren’t getting it from their diet. Additionally, it’s important for those who are suffering from chronic health disorders that results in lowered vitamin D concentrations to consider supplementing their diet."
Duffy MacKay, ND, vice president, scientific and regulatory affairs for the Council for Responsible Nutrition (CRN), said: “Vitamin D is an essential nutrient for good health, and if you’re one of the many people who have low levels of vitamin D, supplementation is a safe and beneficial way to achieve healthy levels. The current Dietary Guidelines for Americans identify vitamin D as one of four nutrients of public health concern because consumers are falling short. Both doctors and consumers should take this into consideration and ensure vitamin D levels are checked during medical check-ups.
"This systematic review is important because it addresses the fact that when people get seriously ill, they often experience nutrient depletions, including low vitamin D levels. When this happens, dietary supplementation should be discussed by the patient and a team of healthcare practitioners because vitamin D is not easily obtained through food, and getting it through sunlight can pose risks—making supplementation a viable option. The authors of the review acknowledge this, specifically the importance of vitamin D supplementation in elderly women who are at risk for falls or fractures. Besides, people who are getting the nutrients they need are likely to respond better to the treatment of their condition—and generally feel better.
“Scientific research demonstrates that vitamin D, in combination with calcium, is critical for the prevention of skeletal diseases, such as osteoporosis. It may be unrealistic to expect vitamin D in isolation from other healthy habits to prevent a disease such as cancer or cardiovascular disease. But we know that one component of disease prevention involves a healthy diet, of which vitamin D is a vital part.”
Ongoing trials
An accompanying editorial in The Lancet Diabetes & Endocrinology said that the odds are stacked against vitamin D being of use in preventing non-skeletal disorders.
“[However] large [ongoing] clinical trials to assess the effects of vitamin D on non-skeletal health outcomes are therefore justified. It would be a real boon to patients if the results are positive, but unless effect sizes for clinically important outcomes are large, the results will only confirm the neutral effect reported by most clinical trials thus far.”
Currently, five big clinical trials are underway testing vitamin D3 for a variety of outcomes in participants over 50 years of age. The table below outlines the trials, the interventions, outcomes and expected completion date.
(Source: K. Kuppferschmidt, Science, 2012, Vol. 337, pp. 1476–7)
Prof Autier and his co-authors concluded: “These studies have the potential to test our hypotheses”.
Source: The Lancet Diabetes & Endocrinology
Published online ahead of print, doi: 10.1016/S2213-8587(13)70165-7
“Vitamin D status and ill health: a systematic review”
Authors: P. Autier, M. Boniol, C. Pizot, P. Mullie