Re: “Is High Dose Vitamin D Harmful?”

Excerpt

Sanders and colleagues [1] reviewed the evidence that high-dose or high serum 25-hydroxyvitamin D (25[OH]D) concentrations might be harmful [1]. It is reasonable that single, large doses of vitamin D might be harmful since they are not physiological doses. However, the evidence regarding possible harm associated with higher serum 25(OH)D concentrations within physiological limits comes from studies with systemic problems that are not generally recognized. The observational studies listed in Table 2 of Sanders et al. [1] were mostly prospective, with serum 25(OH)D concentrations measured at the time of enrollment and long follow-up periods, such as the two pancreatic cancer studies (refs. 79 and 80 in Sanders et al. [1]). A study of lymphoid cancer from the same cohort found an inverse correlation with 25(OH)D for follow-up less than 7 years but a direct correlation for longer follow-up [2]. The findings are also inconsistent with ecological studies with respect to solar UVB doses [3]. The study of esophageal and gastric cancers (ref. 76 in Sanders et al. [1]) was conducted in a region of China with very high rates of these cancers, and the results are inconsistent with ecological studies [3]. The prostate cancer study in Nordic countries (ref. 78 in Sanders et al. [1]) had up to a 17-year follow-up period, and a review of many other prospective studies of prostate cancer found no correlation with respect to serum 25(OH)D concentration at time of enrollment [4]. Ecological studies provide weak support for a role of solar UVB in reducing risk of prostate cancer, and some of the correlations found in the United States may be due to geographical variation or ethnic background [3]. Thus, the seasonal fluctuations of the serum 25(OH)D concentration hypothesis proposed by Vieth (ref. 26 in Sanders et al. [1]) may not be needed. …