An increased intake of vitamin A may result in a decreased risk for bladder cancer, according to the results of a meta-analysis.
An increased intake of vitamin A may result in a decreased risk for bladder cancer, according to the results of a meta-analysis that included 25 studies of dietary or blood vitamin A levels.
However, study authors Jian-er Tang, MD, of Huzhou Teachers College, Zhejiang Province, China, and colleagues pointed out that given the heterogeneity of the studies included in the analysis, it would be premature to recommend an increased intake of vitamin A as a prevention strategy for bladder cancer.
“Vitamin A and retinol are hypothesized to reduce the risk of bladder cancer due to their roles in the regulation of cell differentiation and apoptosis,” the researchers wrote in the World Journal of Surgical Oncology. “A previous meta-analysis, including seven case–control studies and three cohort studies, found no association of bladder cancer in relation with diets low in retinol and beta-carotene.”
However, since that time several more studies of vitamin A, retinol and carotenoids in relation to bladder cancer have been published. Therefore, Tang and colleagues re-examined the literature on the topic in an attempt to calculate more precise risk estimates.
Their analysis included 25 studies published between 1988 and 2013 that included 11,580 cases. Five of the studies measured blood vitamin A levels; three measured plasma vitamin A levels and two measured serum vitamin A levels. In addition, some of the studies included neoplasms of the urinary tracts compared with inclusion of bladder cancer only.
Study results showed inconsistent associations between vitamin A and bladder cancer. The pooled risk estimate for bladder cancer for the highest vitamin A intake compared with the lowest intake was 0.82 (95% CI, 0.65-0.95). Looking at retinal specifically, there was a nonsignificant reduced risk for bladder cancer associated with a high retinal intake (RE = 0.88; 95% CI, 0.73-1.02). However, a high blood level of retinal was significantly linked to a reduced risk for bladder cancer (RE = -.64; 95% CI, 0.38-0.90).
Finally, the meta-analysis also indicated that blood levels of total carotenoids, alpha-carotene, beta-carotene, and lutein and zeaxanthin were all associated with a significant reduction in risk for bladder cancer.
“Although vitamin A is found in a wide variety of foods, many people do not obtain an adequate intake of this nutrient,” the researchers wrote. “Therefore, the impact of vitamin A intake on bladder cancer risk has important public health implications.”