The risk of hip fracture is two to four times higher in stroke patients than in other individuals of the same age, say the authors.
The raised risk is thought to be related to higher levels of the amino acid homocysteine, shown in two studies published last year - one from the Netherlands and the other carried out in the United States - to significantly raise the risk of both hip fracture and other broken bones resulting from osteoporosis.
Both folate and mecobalamin (vitamin B12) reduce homocysteine levels so the team from Mitate Hospital in Tagawa, Japan tested whether these vitamins could reduce fracture risk.
More than 600 patients over the age of 65, who had residual paralysis on one side of the body a year or more after having a stroke, took either 5mg of folate and 1000mcg of mecobalamin daily, or placebos.
During two years of follow-up, the number of falls in each group was virtually the same, but there were only six hip fractures in the supplement group compared with 27 in the placebo group, write Dr Yoshihiro Sato and colleagues in today's issue of the Journal of the American Medical Association (293:1082-1088).
The study also found that bone mineral density did not differ significantly between groups and therefore could not be a cause of the lower number of fractures.
Osteoporotic fractures are a major health problem in Western society and as they are set to increase as the population ages, prevention of fractures is becoming more and more important, points out an accompanying editorial.
Further studies looking at the mechanism for homocysteine's effect on bones will be required before the research can be widely promoted.