Post-menopausal bone loss may be limited by high doses of Vitamin D

Postmenopause: bone loss can be limited thanks to vitamin D

Daily intake of 1000 IU of vitamin D, equivalent to 25 µg, can slow down bone density loss, a very common condition among older women. For lower doses, such as 400 IU daily, vitamin D is not able to provide this protective effect.

This emerges from a study conducted by researchers at the University of Aberdeen, Scotland, published in the Journal of Bone and Mineral Research. The finding supports the decision of the Institute of Medicine (Scotland) to increase the recommended daily dose of vitamin D from 400 IU to 600 IU for children and adults aged 1 to 70 years.

Vitamin D and its functions

Vitamin D is a fat-soluble vitamin that can be introduced into the body through food or synthesized in the human body from a precursor through exposure to sunlight. It exists in several forms, the most common being ergocalciferol (D2) of plant origin, and cholecalciferol (D3) of animal origin. The roles of vitamin D in the human body are various: it is involved in the absorption of calcium and phosphorus in the intestines, modulates immune system function, but above all regulates bone growth, development, and mineralization. The vitamin D requirement varies depending on age and health conditions. In postmenopausal women, for example, vitamin D is very important because the lack of estrogen—which helps regulate calcium absorption and storage in bones—can promote the loss of bone mineral tissue and thus osteoporosis. Vitamin D concentration in the body is measured by detecting one of its metabolites, 25(OH)D (25-hydroxycholecalciferol). Recent studies have shown that the blood concentration of 25(OH)D should be at least 75 nmol/L.

High doses needed to maintain optimal 25(OH)D levels

During the study, 265 women aged between 60 and 70 years were recruited for a one-year trial. One randomly assigned group received 400 IU of vitamin D3 daily, another 1000 IU, and a third received a placebo. After 12 months, the concentration of 25(OH)D was measured in each participant, showing that women taking 1000 IU had an average increase of 42.6 nmol/L of the metabolite. In those taking only 400 IU, the increase was 31.6 nmol/L, while in the placebo group it actually decreased by 4.1 nmol/L. Moreover, there was a loss of bone mineral density at the hip of 0.05% in the group receiving 1000 IU vitamin D, compared to a loss of 0.6% in those receiving the lower dose and placebo. Blood tests one month after the end of treatment revealed that all subjects who received supplementation had a 25(OH)D concentration equal to or greater than 25 nmol/L. However, 40% of the placebo group did not reach this value. The 50 nmol/L threshold was not reached by 16% and 50% of those who took 1000 IU and 400 IU supplements, respectively, and by 94% of the placebo group. The percentage of subjects treated with 1000 IU vitamin D3 who did not reach the 75 nmol/L threshold increased from 48% to 83% thirty days after treatment discontinuation.

Long-term positive effects?

Based on the results, researchers identified that a daily dose of 1000 IU of vitamin D is necessary to bring 25(OH)D to a protective concentration of 76 nmol/L, useful for maintaining bone health and reducing mineral density loss. However, to maintain this circulating 25(OH)D level, treatment should not be discontinued. It remains to be understood whether prolonged supplementation can maintain the positive effects long-term and thus protect the population from vitamin D deficiency risk.

Source: Helen M Macdonald, Adrian D Wood, Lorna S Aucott, Alison J Black, William D Fraser, Alexandra Mavroeidi, David M Reid, Karen R Secombes, William G Simpson, Frank Thies. “Hip bone loss is attenuated with 1000 IU but not 400 IU daily vitamin D3: A 1-year double-blind RCT in postmenopausal women” Journal of Bone and Mineral Research