Hypervitaminosis A: An unrecognized potential risk factor for osteoporosis

Problem: Osteoporosis is a major cause of morbidity and mortality among postmenopausal women and is the most common metabolic bone disorder in the United States. Categorical risk factors for osteoporosis include age, race, gender, lifestyle, genetics, concurrent diseases and the use of select medications. Furthermore, recent research has implicated excess vitamin A as a risk factor for osteoporosis. Even though implications suggest that excess levels of vitamin A may be a forerunner for osteoporosis, it is a necessary vitamin for sustaining a healthy life. The purpose of this literature review is to determine if excess vitamin A is a threat for osteoporosis and to affix a value to "excess" levels. Methods: A PubMed search using the Cornell Medical College Library was conducted for scholarly clinical trials that looked at the relationship between osteoporosis and vitamin A intake. Journal articles that were full text and in English were selected for this literature review. Additional articles generated from this search were used for background information. Results: One review article and 3 studies were selected for this literature review. The results of this research suggest an equivocal relationship between osteoporosis and excess vitamin A. The prospective studies agreed with earlier randomized control animal studies that indicate vitamin A intake in high quantities was associated with osteoporosis. However, the cross sectional studies found no adverse effects of vitamin A on bone. Conclusions: There are wide discrepancies between the outcomes among these studies. These discrepancies are in large part due to poor study design choice. Prospective studies using retinyl esters as a marker for vitamin A status appear to be the most promising approach for future studies. The present inconclusive results warrant further research to determine if excess vitamin A is indeed a risk factor for osteoporosis and, if so, to establish safe upper limits.