Both prediabetes and abnormal blood lipid (cholesterol and triglyceride) levels were linked to an increased risk for major depressive disorder in a new study, published in the American Journal of Psychiatry.
The study authors noted that diabetes has been linked to a higher risk of developing depression in previous studies. Less research, though, has explored the impact of elevated blood glucose — not rising to the level of diabetes — on the risk for mental health disorders. For this study, researchers looked at how three different measures were linked to the risk for major depressive disorder — prediabetes (as measured by fasting plasma glucose of 100 mg/dl or higher), triglyceride to HDL (high-density lipoprotein, or “good”) cholesterol ratio, and central adiposity (belly fat).
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The researchers were interested in how these measurements affected depression risk both when taken at the time of study enrollment, and when looking at how they changed after two years. In both cases, they compared these measurements with the risk of developing major depressive disorder during a follow-up period of nine years. The study participants were 601 people, ages 18 to 65, who took part in the Netherlands Study of Depression and Anxiety (NESDA) and had no personal history of depression or anxiety disorders at the time of study enrollment.
Prediabetes linked to increased risk of major depression
During the follow-up period, 14% of participants developed major depressive disorder. The researchers found that at the time of study enrollment, participants with a high triglyceride-HDL ratio were 89% more likely to develop major depression, while those with prediabetes were 37% more likely to develop major depression. People with high central adiposity — defined by a waist circumference of 100 centimeters (39.4 inches) or greater — were 11% more likely to develop major depression.
When they looked at how participants’ lipid, glucose, and waist measurements changed during the two years after study enrollment, the researchers found only one connection to the risk for major depression. Participants who developed prediabetes during that period were a stunning 166% more likely to develop major depression during the nine years of follow-up, while there was no significant link between developing a high triglyceride-HDL ratio or high central adiposity during those two years and the risk for major depression.
These results reinforce the idea that elevated blood glucose and depression often develop at the same time, the researchers wrote — although it’s unclear if one of these factors directly causes the other. “These findings may have utility for evaluating the risk for the development of major depression among patients with insulin resistance,” they concluded — noting that screening for depression may be helpful well before a person’s blood glucose is high enough to diagnose diabetes.