I have routinely recommended that my patients err on the higher side of D (which sounds like the grade advice I gave to my kids) and that they supplement 1,000 IU’s of Vitamin D a day. (I do). I felt exonerated when I read the report in the July issue of The New England Journal of Medicine that corroborated my suggestion, at least with regards to fracture prevention in women over 65. The authors pooled data from 11 double-blind randomized controlled trials of oral vitamin D with or without calcium. (The participants who were 65 and older were randomly assigned to take Vitamin D and compared to those assigned to control groups). The 11 studies included 31,022 persons (mean age, 76; 91% women) who had 1111 hip fractures and 3770 nonvertebral fractures.
There were both unexpected and expected findings. Although some previous meta-analyses (where multiple studies, not necessarily double-blinded or controlled were combined) suggested that the dose of vitamin D is irrelevant when it is combined with calcium, this pooled analysis did not. On the contrary, the authors found that the risk of fracture with combined supplementation was reduced only at the highest intake-level of vitamin D and moreover, a smaller amount of calcium supplementation (less than 1000 mg per day) was more beneficial in reducing risk of fracture than a larger amount (greater than 1000 mg per day).
They also calculated the difference in fracture rate based on vitamin D supplement doses. This was done by comparing quartiles of vitamin D intake (the lowest, next to lowest, next to highest, as well highest amounts… I feel rather stupid writing it this way, just remember that quartile means a quarter, so they divided the participants into 4 groups according to the amount of Vitamin D they actually took). The risk of fracture decreased only at the highest quartile (800 IU daily), with a 30% reduction in the risk of hip fracture and a 14% reduction in the risk any other nonvertebral fractures. The fracture benefit at the highest level of vitamin D intake was fairly consistent across all age groups, type of dwelling and additional calcium intake.
Bottom line: if you are 65 or older, take at least 800 IU’s of vitamin D a day. And if you are younger (my advice is not a part of this study), get into the habit of making sure you get your D.