Bone loss over 12 months was significantly decreased in women receiving a daily dose of vitamin D of 1,000 IU, but no such effects were seen for 400 IU per day, according to findings published in the Journal of Bone and Mineral Research.
The study, led by researchers from the University of Aberdeen in Scotland, appears to justify the Institute of Medicine’s decision to increase the recommended dietary allowances (RDAs) of vitamin D from 400 IU to 600 IU per day for persons 1 to 70 years of age.
However, the new study appears to be more in agreement with a 2007 editorial by leading vitamin D researchers, which contended that the desirable level of vitamin D in the blood, measured by 25(OH)D, was at least 75 nmol/L. Doses of about 1,700 IU would be needed to raise levels from 50 to 80 nmol/L, they said.
“Our findings are in agreement with the conclusions that more than 400 IU a day may be required to improve bone health and that the mean 25(OH)D concentration at which benefit occurs is greater than 74 nmol/L (mean 25(OH)D reached in our study was 76 nmol/L for the 1000 IU treatment),” wrote the Aberdeen researchers.
“When we excluded women with baseline 25(OH)D greater than 50 nmol/L, which is the threshold above which the Food and Nutrition Board of the Institute of Medicine (IOM) concluded that 97.5% of the population would be vitamin D replete, our findings did not change.”
Kelly Heim, PhD, Pure Encapsulations Nutritional Pharmacologist, told NutraIngredients-USA: "As postmenopausal bone health requires a comprehensive nutritional approach, Vitamin D is seldom considered as a single therapeutic agent. However, these findings underscore the potential impact of a single daily dose of 1,000 IU. The fact that 400 IU was inadequate in these subjects, who all had low levels at baseline, is consistent with other research supporting higher dose requirements. In addition to a significant bone health benefit, this study concurrently provided evidence of bioavailability, as serum levels increased by at least 2-fold within the first two months of supplementation. Taken together, these results suggest that the right vitamin D dose can make a big difference.”
Led by Helen Macdonald, the researchers recruited 305 postmenopausal white women aged 60 to 70 to participate in their double-blind placebo controlled trial. Women were randomly assigned to receive daily vitamin D supplements of 400 IU or 1,000 IU (supplements manufactured by Pure Encapsulations) or placebo for one year.
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.
Data from the 265 women who completed the study indicated, over the course of the year, the 25(OH)D concentrations were found to increase by an average of 31.6 nmol/L and 42.6 nmol/L for the 400 IU and 1,000 IU groups, respectively. The placebo group showed a decrease of 4.1 nmol/L.
In addition, that the mean loss of bone mineral density (BMD) at the hip was negligible in the 1,000 IU group (0.05% loss after 1 year), whereas losses of 0.6% were observed in the 400 IU and placebo groups.
However, there were no significant changes in bone metabolism, added Macdonald and her co-workers.
The need for continued supplementation?
When vitamin D levels were measured one month after the end of the study intervention, the researchers found that 25(OH)D levels for women in both vitamin D groups did not fall below 25 nmol/L, whereas 40% of the placebo group was below this level.
When the higher cut-off of 50 nmol/L was applied – the figure given by the IOM for the majority of the population being replete – the percentage of women with 25(OH)D levels below this value one month after stopping supplementation was 16% and 50% in the 1,000 IU and 400 IU groups, respectively, compared with 94% in the placebo group.
Applying the ‘optimal’ cut-off of 75 nmol/L resulted in even higher numbers of women having 25(OH)D levels falling below this cut off. Indeed, a rapid increase from 48% to 83% of the women in the 1,000 IU group fell below 75 nmol/L within one month of ceasing to take the supplements.
“Although this indicates that the treatment should be continued to sustain 25(OH)D at high circulating concentrations, we do not know if treatment has longer-term benefits in keeping people above the lower threshold for risk of deficiency,” they added.
The study was performed in collaboration with scientists from Woolmanhill Hospital in Aberdeen, the University of East Anglia in England, and Aberdeen Royal Infirmary.
Source: Journal of Bone and Mineral Research
Volume 28, Issue 10, Pages: 2202–2213, doi: 10.1002/jbmr.1959
“Hip bone loss is attenuated with 1000 IU but not 400 IU daily vitamin D3: A 1-year double-blind RCT in postmenopausal women”
Authors: H.M. Macdonald, A.D. Wood, L.S. Aucott, A.J. Black, W.D. Fraser, A. Mavroeidi, D.M. Reid, K.R. Secombes, W.G. Simpson, F. Thies