Madam
It was with great anticipation that the world waited for the release of the recommendations on vitamin D by the Institute of Medicine (IOM), which finally made its debut in November 2010(1). The committee relied on several large meta-analyses including those from the Agency for Healthcare Research and Quality from the USA and Canada as well as larger randomized controlled trials (RCT), and concluded that the previous recommendations made by the IOM in 1997 were woefully inadequate. The committee recognized that, at a minimum, most children and adults should increase their vitamin D intake by 200%, i.e. from 5 to 15 μg vitamin D/d to maintain a healthy skeleton. For adults over the age of 70 years the committee recommended 20 μg vitamin D/d. The committee also appreciated that vitamin D is not as toxic as once thought and therefore doubled the tolerable upper limit from 50 to 100 μg/d for most children and all adults.
There are several thousand publications suggesting that vitamin D deficiency and insufficiency defined as 25-hydroxyvitamin D level <30 ng/ml is a pandemic affecting all populations with serious health consequences(Reference Wang, Pencina and Booth2–Reference Moan, Porojnicu and Dahlback10). However the IOM concluded based on its definition of vitamin D deficiency, i.e. 25-hydroxyvitamin D <20 ng/ml, that this is a relatively rare deficiency in the USA. The IOM only recognized that vitamin D was beneficial for musculoskeletal health and dismissed a multitude of association studies and small RCT suggesting other health benefits, including improving immune and neurocognitive functions(1, Reference Brehm, Schuemann and Fuhlbrigge11, Reference Urashima, Segawa and Okazaki12) and reducing the risk of deadly cancers(Reference Grant13, Reference Lappe, Travers-Gustafson and Davies14), heart disease(Reference Wang, Pencina and Booth2–Reference Dong, Stallmann-Jorgenson and Pollock6), autoimmune diseases(Reference Holick15) and type 2 diabetes(Reference Holick15). The IOM did recognize that many tissues and cells in the body express a vitamin D receptor and that some cells including macrophages have the capability of activating vitamin D locally(Reference Adams and Hewison16). However they did not consider the health implications for why so many cells in the body would have a vitamin D receptor and therefore presumably require 1,25-dihydroxyvitamin D for maximum function and health.
The IOM also suggested based on a few studies that there may be a higher mortality associated with blood levels of 25-hydroxyvitamin D between <20 and >30 ng/ml. However, at least one of the studies it included in the analysis noted there was a lower risk of mortality for 25-hydroxyvitamin D concentrations between 30 and 49 ng/ml and a concentration >50 ng/ml was associated with a higher risk of mortality in women but not in men(Reference Melamed, Michos and Post4).
There have now been several RCT demonstrating that ingesting between 25 and 50μg vitamin D/d and/or attaining a blood level of 25-hydroxyvitamin D >30 ng/ml reduces risk for influenza A infection in schoolchildren(Reference Urashima, Segawa and Okazaki12), reduces vascular stiffness in teenagers(Reference Dong, Stallmann-Jorgenson and Pollock6) and reduces risk of cancer in postmenopausal women by 60%(Reference Lappe, Travers-Gustafson and Davies14). The IOM did not suggest that pregnant and lactating women need more than 15 μg vitamin D/d. However in forty mother–infant pairs where 70% of the women were taking on average 15 μg vitamin D/d, it was reported that 76% of the mothers and 81% of the newborns at the time of birth had 25-hydroxyvitamin D level <20 ng/ml(Reference Lee, Smith and Philipp17); a level considered to be vitamin D deficient by the IOM committee. Furthermore it was reported that pre-eclampsia(Reference Bodnar, Catov and Simhan18) and the need for a primary Caesarean section(Reference Merewood, Mehta and Chen19) were associated with vitamin D deficiency.
There is no downside to increasing vitamin D intake. The IOM in its wisdom in 1997 suggested that all children and adults up to the age of 50 years required only 5 μg vitamin D/d. However, thankfully, it has now realized what most experts have been recommending: that this is totally inadequate to satisfy even bone health. It is likely that, as more RCT are reported using higher doses of vitamin D demonstrating non-skeletal beneficial effects, the next meeting will likely increase the recommendation by another threefold. To achieve a blood level of 25-hydroxyvitamin D >30 ng/ml, children aged 1 year and older should ingest 25 μg vitamin D/d and teenagers and all adults require 50 μg vitamin D/d. A study in Finland reported that children who ingested 50 μg vitamin D/d during their first year of life had substantially reduced risk for type 1 diabetes 31 years later. Therefore the tolerable upper limit should be at least 50 μg/d for this age group(Reference Hypponen, Laara and Jarvelin20). Studies in children and teenagers have demonstrated that 50 μg vitamin D/d is safe and effective in treating and preventing vitamin D deficiency, and therefore a tolerable upper limit of 125 μg/d would be reasonable. Teenagers and all adults should be able to tolerate up to 250 μg vitamin D/d and this would be a reasonable tolerable upper limit.
