Fractured bones are associated with significant morbidity and mortality in the geriatric population; therefore, preserving bone health is a concern for clinicians treating older adults. While inadequate intake of calcium and vitamin D are among the well known dietary risk factors for poor bone health, evidence continues to mount suggesting that too much of another nutrient - vitamin A - may increase fracture risk. The latest results are published in the New England Journal.

Studying Swedish men

In the early 1970s, researchers in Sweden recruited men between the ages of 49 and 51 and followed them for 30 years to determine what, if any, relationship existed between the men's serum levels of retinol (vitamin A) and their risk for subsequent fracture.

Data was collected for 2,322 men, who, at baseline, underwent a detailed evaluation, including filling out medical and lifestyle questionnaires, undergoing anthropometric measurements, and providing serum samples. During follow-up, it was determined that 266 men had suffered bone fractures.

High serum retinol levels related to increased fracture risk

For statistical analysis, the researchers categorized the men into quintiles of serum retinol levels. Those in the highest quintile (>75.62 µg/dL) had a relative risk of 1.64 for fracture compared with men in the middle quintile (62.16-67.60 µg/dL). And among the men in the highest quintile, those with the very highest serum vitamin A levels (99th percentile, >103.12 µg/dL) had a relative risk of 7.14 compared with men in the lower quintiles.

How vitamin A affects bones

The mechanisms by which elevated serum retinol may weaken bones are still under study. The authors suggest it may be that "long-term ingestion of large amounts of vitamin A can lead to hypercalcemia," and that "serum calcium might thus be regarded as having a role in the development of osteoporosis."

Study limitations

Because this study was conducted in a very homogeneous group of subjects, the results cannot necessarily be applied to other racial, ethnic, or age groups, or to women (although previous data from women enrolled in the Nurses' Health Study indicate an association between high vitamin A intake and increased risk for hip fracture). It's also important to note that a weakness of the study, which may have influenced the results, is that the subjects' serum retinol levels were measured only once, at the beginning of the study, and there was a long interval between measurement and follow-up. There is no way to know how stable vitamin A levels remained over time.

Screening patients for retinol levels

The results of this study alone do not warrant the widespread screening of serum retinol levels, but they do indicate that a high intake of vitamin A may serve as a "red flag" when clinicians are assessing patients' bone health.

The recommended daily intake of vitamin A is 700 µg for women and 900 µg for men. Vitamin A is found primarily in animal foods, such as liver, fish, eggs, and milk, as well as in some fortified foods, such as cereals and energy bars.

It is also important to note that the research does not indicate an association between increased fracture risk and intake of beta-carotene, which is found primarily in plant foods and is converted to vitamin A in the body. An antioxidant nutrient, beta-carotene may help protect against cancer and preserve eye health. It is found in dark green and orange fruits and vegetables, such as sweet potatoes, carrots, cantaloupe, and leafy greens.