Calcium supplement use to prevent osteoporotic fractures is common among the general public, explains Gang Liu, PhD. “While the association between calcium supplements and cardiovascular disease (CVD) risk in the general population is debatable, evidence is scarce among people with diabetes who are at higher risk for both abnormal calcium metabolism and CVD,” Dr. Liu says. “Therefore, addressing these controversies and filling gaps in knowledge is crucial for evidence-based clinical recommendations.”

For a study published in Diabetes Care, Dr. Liu and colleagues aimed to assess the link between habitual calcium supplements and CVD events and mortality in people with and without diabetes. Additionally, they examined the associations of dietary and serum calcium with CVD events and mortality in people with and without diabetes.

Using a large population-based cohort with comprehensive data, the study included 434,374 participants (21,676 with diabetes) with a mean age of 56. To estimate HRs and 95% confidence interval, the researchers used Cox proportional hazards regression models. Interactions between diabetes status and calcium supplement were measured via multiplicative and additive scales.

Calcium Supplements Linked With All-Cause Mortality in People With Diabetes

The study team observed that in people with diabetes, habitual calcium supplement use was significantly linked with higher risks for CVD incidence (HR, 1.34; 95% CI, 1.14-1.57), CVD mortality (HR, 1.67; 95% CI, 1.19-2.33), and all-cause mortality (HR, 1.44; 95% CI, 1.20-1.72). No significant correlation was noted in people without diabetes for CVD incidence (HR, 0.97; 95% CI, 0.92-1.03), for CVD mortality (HR, 1.05; 95% CI, 0.90-1.23); or for all-cause mortality (HR, 1.02; 95% CI, 0.96-1.09).

Additionally, the researchers observed a decreased risk for CVD events and all-cause mortality solely among people with moderate calcium intakes (approximately 900-1000 mg/day), with and without diabetes.

Notable additive and multiplicative interactions were revealed between habitual calcium supplement use and diabetes status on the risk for CVD events and all-cause mortality, according to Dr. Liu and colleagues (Table). Three measures of additive interaction between calcium supplements and diabetes showed that the risk for CVD and mortality in people with both risk factors (diabetes and habitual calcium supplementation) was 0.44 to 1.11 times higher as a result of the additive interaction, and 2.18 to 2.96 times higher than the sum of risks in people exposed to a single risk factor.

Calcium-Rich Foods Are Safer Than Supplementation

“Our finding indicated that people with diabetes might need to use caution when it comes to long-term use of calcium supplements,” Dr. Liu says. He adds that further studies are needed to better understand the benefits versus the adverse effects of calcium supplementation, particularly among people with diabetes. “Meanwhile, a safe alternative to calcium supplements is to consume calcium-rich foods, such as low-fat dairy foods, green leafy vegetables, and beans, which contain not only calcium but also essential minerals and vitamins,” he says.

Incorporating the findings of the study into clinical practice would involve adopting an individualized approach, Dr. Liu adds. “Physicians should assess each patient’s diabetes status, cardiovascular risk factors, and bone health to determine whether calcium supplementation is appropriate and at what dosage,” he says. “Until further studies become available, calcium supplements should be restricted to patients with diabetes who are unable to meet the required higher amounts of calcium intake through diet alone. Initiation of long-term calcium supplementation in these patients should follow a careful discussion of potential benefits and harms.”