Vitamin D, PTH, and calcium and the risk of prostate cancer: a prospective nested case-control study.

OBJECTIVE:
To examine the risk of prostate cancer in relation to pre-diagnostic serum levels of vitamin D (25OHD(2) and 25OHD(3)), PTH, and calcium.

METHODS:
Nine hundred forty-three incident prostate cancer cases were identified in the Malmö Diet and Cancer Study cohort, and each was matched with one control using incidence density matching with age as the underlying timescale. We also matched for calendar time and age at inclusion. Logistic regression analysis yielded odds ratios with 95 % confidence intervals for different quartiles and deciles. All analyses were repeated stratified for age and body mass index (BMI).

RESULTS:
We found a weak trend toward increasing prostate cancer risk with rising vitamin D levels (p-trend across quartiles, 0.048). Dividing the cohort into deciles showed a nonlinear association. Compared to decile one, the prostate cancer risk was highest in deciles seven and eight, which corresponded to vitamin D levels of 91-97 nmol/L (1.68; 1.06-2.68), and 98-106 nmol/L (1.80; 1.13-2.85). In the other deciles, there was no association between prostate cancer risk and vitamin D levels. Albumin-adjusted calcium was positively associated with an increased risk for prostate cancer among men aged 55-65 with a BMI <25 (2.07; 1.08-3.97). No association was observed between pre-diagnostic PTH and subsequent prostate cancer incidence, and the stratified analyses revealed no other convincing relationships.

CONCLUSIONS:
This study suggests a possible weak positive nonlinear association between vitamin D and the risk of prostate cancer.