Vitamin A intake and osteoporosis: a clinical review.
BACKGROUND
If osteoporosis is linked with vitamin A (Vit A) A consumption, millions of people could be affected.


METHODS
A MEDLINE search was performed with keywords retinol, beta-carotene, and osteoporosis.


RESULTS
Of 20 clinical studies, 3 were randomized controlled trials (RCTs), 14 were observational studies, and 3 were case reports. Most (8) observational studies were cross-sectional. Oral retinoyl palmitate (RP) in high doses induces fractures and radiographic osteoporosis in animals. Retinol intake from diet or supplements is negatively associated with lumbar, femoral neck, and trochanter bone mineral density (BMD). There is a graded increase in relative risk of hip fracture with increasing retinol intake, attributable primarily to retinol (either from diet or supplements) but not beta-carotene intake. Higher serum retinol levels are associated with higher risk of any fracture and with higher risk of hip fracture, whereas there is no evidence of harm associated with beta-carotene intake. The few RCTs involve serum markers of bone metabolism, not bone density or fracture outcomes. Observational studies are generally consistent in finding harm from either dietary or supplemental retinol intake on BMD and hip fracture risk. Total Vit A intake is more important than source in determining harm. Adverse effects may occur at a level of retinol intake that is only about twice the current recommendation for adult females.


CONCLUSIONS
It is not yet possible to set a specific level of retinol intake above which bone health is compromised. Pending further investigation, Vit A supplements should not be used with the express goal of improving bone health.
Crandall
Carolyn
C
Department of Medicine, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California 90095-7023, USA. ccrandall@mednet.ucla.edu
D000368:Aged; D000818:Animals; D015992:Body Mass Index; D015519:Bone Density / Q000187:drug effects*; D001842:Bone and Bones / Q000187:drug effects; D015331:Cohort Studies; D005260:Female; D050723:Fractures, Bone / Q000097:blood / Q000209:etiology*; D006620:Hip Fractures / Q000209:etiology; D006801:Humans; D008297:Male; D010024:Osteoporosis / Q000097:blood / Q000139:chemically induced* / Q000517:prevention & control; D011322:Primary Prevention / Q000592:standards; D016032:Randomized Controlled Trials as Topic; D012307:Risk Factors; D013997:Time Factors; D014481:United States; D014801:Vitamin A / Q000008:administration & dosage / Q000009:adverse effects* / Q000097:blood*; D019207:beta Carotene / Q000009:adverse effects*
D019207:beta Carotene; D014801:Vitamin A