Purpose: Vitamin D, parathyroid hormone (PTH) and calcium in blood are correlated with each other. Previous studies have suggested vitamin D to have anti-proliferative effects on tumor cells, whereas PTH may have carcinogenic effects. A cancer disease may influence calcium levels in blood, but less is known about calcium and its potential effect on cancer risk and survival. The aim of this study was to examine pre-diagnostic levels of vitamin D (25OHD), PTH and calcium in relation to survival after breast cancer.
Methods: The Malmö Diet and Cancer Study enrolled 17,035 women between 1991 and 1996. 672 patients developed incident invasive breast cancer up until 31 December 2006. Serum samples collected at baseline were analyzed for 25OHD, PTH and calcium. All patients were followed until 31 December 2010 using the Swedish Cause of Death Registry. The analytes were divided into tertiles and the risk of death from breast cancer was analyzed using an adjusted Cox proportional hazards analysis, yielding hazard ratios with 95 % confidence intervals.
Results: Levels of 25OHD and breast cancer mortality were associated in a u-shaped manner with the highest mortality among patients in the first (2.46: 1.38-4.37) and third tertiles (1.99: 1.14-3.49), as compared to the second. An inverse relation was found between calcium levels and breast cancer mortality, with the lowest mortality in the third tertile, (0.53: 0.30-0.92) as compared to the first. There was no clear association between PTH and breast cancer mortality.
Conclusions: This study shows that pre-diagnostic 25OHD and calcium may affect survival following breast cancer.