In 2002, Harvard researchers published a report that seemed to indicate that long-term supplementation of pre-formed vitamin A (retinol, not beta-carotene) increases risk for osteoporosis and fractures in postmenopausal women (CLICK HERE for article). This data seemed to confirm some previous observations in animal studies, although there have since been other epidemiological studies which showed no correlation between the intake of pre-formed vitamin A and fracture risk in women (see below). Regardless, after 2002, it has been commonly advised by most guidelines to limit daily retinol consumption (below 7,500 IU/day- although some have said less than 5,000 IU) to limit the potential fracture risk. Many nutritional products were adjusted at that time to increase beta-carotene and reduce retinol to make vitamin A claims.
The relationship between vitamin A intake and fracture risk was analyzed in a post-hoc analysis of the data from the Womens Health Study. The data from this large clinical trial showed no relationship between vitamin A intake and fracture risk except in women with vitamin D deficiency (CLICK HERE for article). Subjects with the lowest vitamin D intake ( less than 440 IU per day) in the highest quintile of vitamin A intake (greater than 8,250 IU of retinol per day) had an increase risk of total fractures of 15%. However, in subjects consuming greater than 440 IU per day of vitamin D, no increased risk was noted at any dose of retinol or other vitamin A intake.
These data need to be confirmed by more targeted clinical trials, but this confirms the understood relationship between vitamin A and vitamin D; especially as it relates to bone metabolism. While it may be too early to eliminate the vitamin A restrictions put in place in 2002, it emphasizes the importance of ensuring elevated vitamin D intake, which may make these restrictions irrelevant.