Background: Observational studies have shown a positive association between intake of dairy products as well as serum levels of calcium and prostate cancer (PCa) risk. We studied the association between serum calcium and PCa while also accounting for levels of albumin, a protein to which calcium is bound.
Methods: A cohort based on 196,022 men with baseline information on calcium (mmol/L) and albumin (g/L) was selected from the Swedish Apolipoprotein MOrtality RISk study. Age-stratified multivariable Cox proportional hazard models were used to analyze associations between calcium and incident and fatal PCa risk.
Results: A total of 6,353 men were diagnosed with PCa and 731 died of PCa during mean follow-up of 12 years. A weak negative association was found between levels of calcium or albumin-corrected calcium and PCa risk (HR for quartiles of albumin-corrected calcium: 0.95 (0.89-1.02), 0.93 (0.86-1.00), and 0.91 (0.85-0.98) for the 2nd, 3rd, and 4th quartile compared to the 1st; p for trend: 0.012). BMI did not affect these findings. No association was found between calcium levels and fatal PCa. A positive association between Ca and death was observed when censoring for PCa [HR per SD: 1.14 (1.13-1.16)].
Conclusion: The weak negative association between Ca and PCa risk is likely explained by the relation between Ca and death. This illustrates the need to handle competing risks when defining whether Ca is involved in PCa etiology or whether it acts as a marker of other metabolic events in the causal pathway.