Daily supplements of the vitamin were especially effective in winter, when sunlight levels are significantly reduced, according to results of the population-based, double-blind, randomised controlled trial published in the Archives of Internal Medicine.
"Ergocalciferol, 1000 IU/d, added to a high calcium intake is associated with 23% reduction of the risk of falling in winter/spring to the same level as in summer/autumn," wrote lead author Richard Prince from the Sir Charles Gairdner Hospital, Australia.
"Thus, we propose that 25(OH)D levels averaging 21.7 ng/mL should be considered as adequate to prevent the risk of falling owing to vitamin D deficiency in elderly women living in the community."
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol.
The former is produced in the skin on exposure to UVB radiation (290 to 320 nm).
The latter is derived from plants and only enters the body via the diet.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 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.
Gairdner and co-workers recruited 302 community-dwelling women (average age 77.2) years living in Perth, Australia (latitude, 32 degrees south), and randomly assigned them to receive either 1000 IU per day of vitamin D2, or placebo for one year.
All the women also received daily calcium citrate supplements (1,000 mg).
The women all had baseline blood levels of 25(OH)D of less than 24 nanograms per millilitre, and reported a history of previous falls.
After 12 months of supplementation, the researchers report a significantly more falls in the placebo group than in the vitamin D2 group (62.9 versus 53 per cent, respectively).
Moreover, the risk of falling in winter, when sunlight levels are at their weakest, was significantly reduced as a result of vitamin D2 supplementation, compared to placebo - the risk of having a first fall in winter was 25.2 per cent for D2, compared to 35.8per cent in the placebo group.
"When those who fell were grouped by the season of first fall or the number of falls they had, ergocalciferol treatment reduced the risk of having the first fall in winter and spring but not in summer and autumn, and reduced the risk of having one fall but not multiple falls," wrote the authors.
The results are also interesting given recent questions over the efficacy of D2 versus D3.
Indeed, several studies have reported that vitamin D2 is between 30 and 50 per cent less effective as the D3 form in maintaining blood levels in humans.
"It should be noted that our study used ergocalciferol rather than cholocalciferol," wrote Prince and co-authors.
"Ergocalciferol has been reported to be less potent, unit for unit, in maintaining 25OHD levels in the circulation; therefore, the effect of vitamin D3 on reduction of falls could be greater."
However, a recent study, published in the Journal of Clinical Endocrinology & Metabolism , reported that supplementation with both forms produced similar results.
Source: Archives of Internal Medicine 14 January 2008, Volume 168, Issue 1, Pages 103-108 "Effects of Ergocalciferol Added to Calcium on the Risk of Falls in Elderly High-Risk Women" Authors: R.L. Prince, N. Austin, A. Devine, I.M. Dick, D. Bruce, K. Zhu