A recently published study in the American Journal of Clinical Nutrition investigated the relationship between serum calcium concentrations and incident diabetes.
Ninety percent of calcium in the body is located within the skeleton. Found in dairy products and dark green leafy vegetables, calcium is a mineral that provides structural support and helps maintain calcium balance through extra-skeletal exchange. Since calcium is often viewed in connection to bones, it’s no surprise that most traditional reviews on calcium have been in relation to bone health. However, recent studies have suggested that an increased concentration of calcium in the serum – the clear liquid that can be separated from clotted blood – may be associated with a greater risk for type 2 diabetes.
Type 2 diabetes is a disease characterized by abnormal glucose metabolism. Typically, the pancreas produces insulin, a hormone that allows cells to turn glucose from food into energy. With type 2 diabetes, the pancreas either does not produce enough insulin, or it does not properly use the insulin it makes. This results in glucose build-up in the blood instead of it being used for energy.
However, the previous studies that investigated the association of serum calcium concentration and type 2 diabetes did not report any information on 25-hydroxyvitamin D or parathyroid hormone (PTH), two factors that are involved in regulating serum calcium. Calcium-sensing receptor (CaSR), expressed in the parathyroid glands and kidneys, helps regulate serum calcium concentration by secreting parathyroid hormone and reabsorbing calcium. More specifically, an increase in serum calcium activates the calcium-sensing receptor. The receptor then decreases the secretion of PTH. The decreased PTH secretion results in a decreased resorption and reabsorption of calcium in the bones and kidneys, as well as a decreased synthesis of 25-hydroxyvitamin D. A decreased synthesis of 24-hydroxyvitamin D then results in decreased calcium absorption.
Genome studies have also found that a single nucleotide polymorphism (SNP) – a variation in a base pair in a DNA sequence – within the CaSR gene was associated with serum calcium concentration in individuals with European ancestry. But since previous studies on serum calcium and type 2 diabetes have had limited racial-ethnic diversity, scientists are unsure whether serum calcium and incident diabetes may vary by race, considering that diabetes is more highly prevalent in blacks than in whites.
A study published in the American Journal of Clinical Nutrition sought to delve deeper into these possible relationships. Is an increase in serum calcium concentration associated with a greater risk for type 2 diabetes? Do PTH and 25-hydroxyvitamin D play a role in this association? Is this association independent, or does the DNA sequence variation in the CaSR of those of European descent play a role? Are certain races at a higher risk for incident diabetes due to an increase in serum concentration?
For the study, scientists investigated a total of 12, 800 participants from the Atherosclerosis Risk in Communities (ARIC) study. The ARIC study includes individuals who were between the ages of 45 to 65 years old in 1987-1989, and were required to attend four clinic examinations between the years of 1990 and 2013. Investigators collected demographic characteristic, medical history and lifestyle habit information from the participants. At each clinical visit, participants also provided blood samples. Researchers measured calcium from the serum, and also measured glucose, PTH and 24-hydroxyvitamin D in the serum or plasma. Doctors diagnosed participants with incident type 2 diabetes as it occurred.
The researchers found that an increase in serum calcium is indeed associated with a greater risk for type 2 diabetes. They also note that PTH and 25-hydroxyvitamin D may not fully capture the relationship between calcium and diabetes. The data also revealed that the DNA sequence variation in the CaSR was not associated with diabetes risk in whites. The researchers also did not find any statistically significant race interactions in relation to serum calcium and diabetes, but they do observe that this association is stronger among blacks than among whites. The study concludes that “further research is needed to understand the role, if any, that calcium plays in the pathogenesis of diabetes.”
Written By: Jessica Gelar, HBSc