A study of 36,000 women, half of whom took a gram of calcium and 400 IU of vitamin D for a period of 7 years was recently published in the Journal of the National Cancer Instutute
The main findings do not support a causal relationship between calcium and vitamin D supplement use and reduced breast cancer incidence, despite the association observed in some epidemiological studies
Commentary: When I see studies like this, its hard to know whether the authors are just uninformed, or actually malicious. OF COURSE there was no difference in breast cancer incidence from taking a gram of calcium and 400 IU of vitamin D (the calcium is mostly irrelevant, its the vitamin D that is important in cancer prevention). There is a very rich scientific literature about vitamin D that has appeared over the past decade, which these authors apparently have not been reading. Given that somewhere between 50 and 80% of adults in the US are vitamin D deficient or insufficient (levels below 30 ng/ml), and that during the wintertime, taking even 1000 IU of vitamin D a day will not raise the blood level of 25-hydroxy vitamin D above 30 ng/ml (recently published by Dr. Michael Holick), drawing conclusions from a study in which 18,000 women took 400 IU of vitamin D is ludicrous! Now if they had given these women 4,000 IU of vitamin D instead of 400, its very likely that they would have seen very different results. In fact, a study by Lappe et al reported that postmenopausal women who took 1100 IU of vitamin D3 a day for 4 years (along with calcium) showed a 60% reduced risk of developing all cancers compared to a group with similar cancer risk factors that took placebo. So just because a study is in the Journal of the National Cancer Institute, don’t assume that its authors know what they’re talking about!