Serum 25-hydroxyvitamin D, dietary calcium intake, and distal colorectal adenoma risk

Vitamin D has recently emerged as a potentially protective agent against co lorectal neoplasia. We assessed the associations between dietary vitamin D, plasma 25-hydroxyvitamin D [25(OH)D], dietary calcium, and colorectal aden omas in a large screening sigmoidoscopy-based case-control study in Souther n California. Because conversion of serum 25(OH)D to serum 1,25-vitamin D i s highly regulated by serum calcium, we also assessed modification of the 2 5(OH)D-adenoma association by calcium intake. Cases were 473 subjects with a primary adenoma, and controls were 507 subjects who had no adenomas at si gmoidoscopy and no history of adenomas. Compared with those in the lowest q uartile of intake, those in the highest quartile of dietary vitamin D had a n adjusted odds ratio (OR) of 0.83 [95% confidence interval (CI) = 0.49-1.4 1] and those in the highest quartile of dietary calcium had an OR of 0.82 ( 95% CI = 0.49-1.25). There was a suggestion that plasma 25(OH)D maybe prote ctive in this population (OR for highest vs. lowest quartile = 0.74, 95% CI = 0.51-1.09). A significant protective effect of 25(OH)D was clearly evide nt only in those with calcium intakes below (OR = 0.40 for highest vs. lowe st quartile, 95% CI = 0.22-0.71, p for trend = 0.005) and above (OR = 1.17, 95% CI = 0.69-1.99, p for trend = 0.94) the median calcium intake.