Back in December, one of my blogs focused on research which sought to determine the intakes of vitamin D required to maintain certain concentrations of this nutrient in the body [1]. This particular study found that to maintain a vitamin D level of 80 nmol/L (32 ng/ml) about 1600 IU is required. You can read the whole blog post here.
Some regular readers may know that I have, for the last few months, been attempting to optimise my own vitamin D levels. Earlier in the year, I had my levels measured for the first time ever and these came back at 15 ng/ml (very low). I started supplementing with vitamin D at a dose of 3000 IU per day and about 10 weeks later, my levels had increased to 31 ng/ml. The 3000 IU I was taking was roughly twice what I theoretically needed to maintain this level of vitamin D [1]. Perhaps my need for vitamin D was greater than others? Reading a letter published on-line in the American Journal of Clinical Nutrition this week, I’m not so sure.
In this letter [2], Dr Reinhold Vieth from Mount Sinai hospital in Toronto criticises the mathematical extrapolation on which previous research [1] was based. Dr Vieth claims that this inappropriate methodology has led to an underestimation in vitamin D requirements. In support of this he cites three studies (two, his own) in which individuals were actually supplemented with vitamin D to see what blood levels were achieved [3-5]. According to this research (in both younger and older adults), to maintain a blood level of 32 ng/ml requires 4000 IU (100 mcg) of vitamin D per day.
These levels are much more in line with my own, recent experiences. But much more importantly, they again demonstrate that the traditionally recommended vitamin D levels are quite inadequate. 4000 IU per day is 10 times the amount usually recommended, and this is to achieve a blood level that some would stay is still a way off optimal.
References:
1. Cashman KD, et al. Estimation of the dietary requirement for vitamin D in healthy adults. Am J Clin Nutr 2008;88:1535-1542.
2. Vieth R. Experimentally observed vitamin D requirements are higher than extrapolated ones. Am J Clin Nutr 26th August 2009 [epub ahead of prin publication]
3. Vieth R, et al. Randomized comparison of the effects of the vitamin D3 adequate intake versus 100 mcg (4000 IU) per day on biochemical responses and the wellbeing of patients. Nutr J. 2004;19;3:8.
4. Vieth R, et al. Efficacy and safety of vitamin D3 intake exceeding the lowest observed adverse effect level. Am J Clin Nutr. 2001;73(2):288-94.
5. Mocanu V, et al. Long-term effects of giving nursing home residents bread fortified with 125 microg (5000 IU) vitamin D(3) per daily serving. Am J Clin Nutr. 2009;89(4):1132-7.
