Background: Primary hyperparathyroidism (HPT) is a disease characterized by hypercalcemia, and associated with an increased mortality in cardiovascular diseases. However, serum calcium levels within the normal range have not been evaluated as a prospective cardiovascular risk factor.
Methods: A cohort of males aged 50 (n = 2183) were investigated in 1970-1973 for serum calcium and known cardiovascular risk factors. They were then followed up over the next 18 years.
Results: During the follow-up period, 180 subjects experienced a myocardial infarction (MI). The serum calcium levels were significantly elevated at the baseline (2.37 +/- 0.09 SD versus 2.35 +/- 0.09 mmol/l, p < 0.03) in the subjects who developed a MI when compared with the rest of the cohort. Also blood pressure, body mass index (BMI), fasting insulin, serum cholesterol, serum triglycerides, and the atherogenic index were significantly elevated in the MI group (p < 0.01), while HDL-cholesterol was lower at the baseline investigation (p < 0.01). Cox's proportional hazard analysis showed that only serum calcium (p < 0.01), BMI (p < 0.0003), diastolic blood pressure (p < 0.0009), and the atherogenic index (p < 0.002) were significantly independent risk factors for MI. The range of serum calcium levels from the mean value, -2 SDs to the mean value +2 SDs corresponds to a variation in estimated risk for MI ranging from 0.06 to 0.15.
Conclusions: Serum calcium was found to be an independent, prospective risk factor for MI in middle-aged males suggesting a role for extracellular calcium levels in the atherosclerotic process.