The use of vitamin D supplements to reduce the risk of osteoporosis in healthy adults is ‘inappropriate’, says a new meta-analysis from New Zealand, but such claims should not discourage healthy people from taking vitamin D for all the possible benefits, says the Council for Responsible Nutrition.
The meta-analysis, published in The Lancet , used data from 23 studies involving 4082 healthy adults (average age 59 years), and found that vitamin D supplements over an average period of two years did not produce any bone health benefits, except for a small but statistically significant increase in bone density (0.8%) at the femoral neck. Such a localised effect is unlikely to be clinically significant, said the researchers, led by Professor Ian Reid from the University of Auckland in New Zealand.
“In the past few years, some clinicians have been enthusiastic about use of vitamin D supplements in doses of more than 1000 IU per day, with a view to achieve serum 25hydroxyvitamin D concen trations greater than 75 nmol/L,” they wrote. “Our analysis gives no support for this target concentration of 25hydroxyvitamin D, because the existing evidence of benefit on bone mineral density comes from doses of 400–800 IU per day.
“In fact, data from studies comparing highdose with lowdose vitamin D supplements suggest that individuals on a low dose have improved bone mineral density, although differences between the groups were not significant.
“Although these conclusions contrast with those of many advocates in the specialty, they align well with the 2010 report from the Institute of Medicine, which concluded (partly on the basis of histological evidence) that 40 nmol/L was an adequate concentration of serum 25hydroxyvitamin D, and that most adults in North America do not need supplementation.”
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. Recently, data has also suggested that vitamin D deficiency and vitamin D insufficiency (between 21-29 ng/mL) may be linked to cancer, autoimmune diseases, infectious diseases, type 2 diabetes and cardiovascular disease.
However, in response to the findings, and the conclusions that vitamin D supplements may be ‘inappropriate’, Duffy MacKay, N.D., vice president, scientific and regulatory affairs at the Council for Responsible Nutrition (CRN), said: “We feel just as strongly that this meta-analysis not discourage healthy people from taking vitamin D for all the possible benefits. Beyond osteoporosis and bone health, vitamin D provides extensive benefits in other areas.
“The body of scientific literature, including new and emerging research, shows vitamin D plays an important role in cardiovascular health, immune health and diabetes; therefore, it is vital that doctors and other healthcare practitioners continue to test vitamin D levels.
“Because vitamin D is not easily obtained from food, and obtaining it through sunlight carries cancer risks, replenishing through supplementation is a safe and appropriate way to get vitamin D."
Dr MacKay added that the scientific literature supports that vitamin D is necessary for calcium absorption and bone density, and therefore the two nutrients work in combination to provide a protective effect for helping to prevent osteoporosis. “One of the serious limitations of this meta-analysis was the lack of consideration of studies that looked at how vitamin D and calcium work together,” he said.
“For populations that are most vulnerable to vitamin D deficiencies and insufficiencies—especially older adults—getting vitamin D from food alone is particularly challenging, and so supplementation may be warranted.
“We have concerns that the author’s broad-based advice will do nothing but cause potentially dire consequences if people, particularly those at-risk for fracture, fail to obtain the recommended daily intake of vitamin D.”
Recommended dietary intakes from the Institute of Medicine for adults are 600-800 IU of vitamin D and 1000-1300 mg of calcium daily, he added, and the 2010 Dietary Guidelines for Americans identifies supplements containing combinations of certain nutrients such as calcium and vitamin D as useful in postmenopausal women who have low levels of these nutrients in their diets to reduce the risk of osteoporosis.
“In addition, the Food and Drug Administration has an approved health claim for calcium, vitamin D and osteoporosis,” said Dr MacKay.
Dr Carrie Ruxton from the Health Supplements Information Service in the UK said: “Vitamin D is essential for maintaining strong and healthy bones and preventing diseases like rickets, osteoporosis, and cardiovascular disease, yet 75% of the UK population has a vitamin D intake below the recommended level. At particular risk are children and the elderly.”
“It is unsurprising that this meta-analysis found no significant impact of vitamin D when taken alone. In terms of bone health, vitamin D promotes calcium absorption and its utilisation by bone, having the strongest impact on bone density when taken alongside dietary calcium.
“In the present meta-analysis, only half of the trials used both calcium and vitamin D supplementation. In trials in which vitamin D was given simultaneously with calcium, a significant reduction of 11% in hip fractures and a very modest increase in hip bone mineral density was reported.”
De Ruxton added that the UK National Diet and Nutrition Survey found that only 2% of adults (19-64 years) and 4% of elderly people (65+ years) took vitamin D + calcium supplements, whereas 5% took multivitamins (3% in elderly). "This Lancet study which suggests that half of adults take vitamin D supplements, provides a gross overestimate for supplement use in the UK,” she said.
“Overall these findings from the Lancet study cannot easily be applied to the UK where unlike in sunnier climates such as Australia and large parts of the USA, vitamin D deficiency continues to be a major problem. Up to a quarter of adults have inadequate blood vitamin D levels, according to Government data. This is due to our turbulent weather and dark winters, which restrict how much vitamin D our bodies can make, as well as low intakes of oily fish (the best natural source of vitamin D). It is also worth remembering that vitamin D is needed for more than bone health. Emerging evidence suggests a role in immune function, maintenance of heart health and even prevention of chronic conditions such as multiple sclerosis and diabetes.”
Source: The Lancet
Published online ahead of print, doi: 10.1016/S0140-6736(13)61647-5
“Effects of vitamin D supplements on bone mineral density: a systematic review and meta-analysis”
Authors: I.R. Reid, M.J. Bolland, A. Grey