Tonight my husband texted me this photo, from ScienceDaily (read the first two headlines):
I was amused.
“Sometimes science is confusing”, I texted back.
After all, it’s often difficult to compare two different studies testing the same variable, due to differing parameters like sample size, dose, subject profiles, etc. I thought about how science headlines often become so distilled we lose the meaty complexity that made the story a headline in the first place.
And then I went to Science Daily and realized these headlines referred TO THE EXACT SAME STUDY.
The study is entitled, “Effect of Vitamin D and Calcium Supplementation on Cancer Incidence in Older Women”, and was published today in JAMA, the Journal of the American Medical Association.
The JAMA abstract states that:
“in this randomized clinical trial of 2303 healthy postmenopausal women with a mean baseline serum 25-hydroxyvitamin D level of 32.8 ng/mL, supplementation with vitamin D3 and calcium compared with placebo did not significantly reduce the incidence of all-type cancer over 4 years of follow-up.”
The ScienceDaily summary also presents this conclusion, and goes on to explain that after four years of supplementing a treatment group with vitamin D and calcium, and monitoring a placebo group, there was no statistically significant difference in cancer diagnoses between the treatment and placebo groups. 3.89% of individuals in the treatment group received a cancer diagnosis over the four years, compared with 5.58 % in the placebo group. As prior evidence suggests low vitamin D levels may increase the risk of cancer, the summary states the authors of the study suggest higher baseline vitamin D levels in the subjects, as compared with the U.S. population, as one reason for the lack of statistically significant results.
The summary underneath the next ScienceDaily headline, again, ON THE SAME STUDY, states that supplementing with vitamin D and calcium may lower risk for developing cancer, and states that “women who were given vitamin D3 and calcium supplements had 30% lower risk of cancer.” The summary then goes on to state that, “this difference in cancer incidence rates between groups did not quite reach statistical significance,” but, that “in further analyses, blood levels of vitamin D, specifically 25-hydroxyvitamin D (25(OH)D), were significantly lower in women who developed cancer during the study than in those who remained healthy.”
The second summary goes on to state that one of the researchers said the study suggested that higher levels of vitamin D are are associated with lower cancer risk.
This additional claim is not made in the JAMA summary, which feels surprising as it’s the kind of result you’d think the research community would want to tout. In addition, this second summary is actually a press release put out by the university where the study was conducted.
My question: when were the further analyses done? As part of this study? In a separate study? My inquiring mind wants to know. So, I will be reading the ACTUAL STUDY this week and getting to the bottom of it.