“One in three people has insulin resistance in the United States,” says Dr. Shabani Sethi, a double board-certified psychiatrist and obesity medicine physician at Stanford University School of Medicine. She emphasizes how this condition doubles a person’s risk of depression. But how are they connected? Let’s dive deeper.
What is insulin resistance?
Insulin resistance is a condition in which the body doesn’t respond to insulin the way it should. Insulin is a hormone produced by the pancreas and is essential for regulating blood sugar levels.
Insulin resistance can lead to elevated blood glucose levels and weight gain. If someone has blood glucose levels that are higher than normal but not high enough to be diagnosed as type 2 diabetes, they have prediabetes. If the blood glucose levels continue to go up, you could develop type 2 diabetes, which can affect almost every part of your body, including your heart, eyes, kidneys, and nerves.
How is insulin resistance linked to depression?
Dr Sethi is the founding director of Stanford’s groundbreaking new field, the Metabolic Psychiatry Program, where she unites nutrition, metabolism, and mental health care. “One in three people has insulin resistance in the United States, and that doubles your risk of developing depression, even if you have had no psychiatric history,” she told Dr. Mark Hyman, a leading functional medicine doctor, on his podcast. Explaining about the new field of metabolic psychiatry, Dr. Sethi said, “Metabolic psychiatry is thinking about metabolism and mental health connection, but it’s the study of all of the metabolic dysfunctions, both systemic as well as central. So you can have dysfunction in the brain, and you can have dysfunction outside the brain in the body. And those two elements are important in thinking about how that affects psychiatric disease and mental health.”So, how is insulin resistance connected to mental illness? “In primary care, I saw a lot of patients who had diabetes or hypertension. But the folks who had the more severe depression tended to have insulin resistance, or they had some other metabolic condition. Those with diabetes who weren’t doing well had depression,” she said. “In bipolar illness, about 37-40% have metabolic syndrome,” she added. “If you have insulin resistance, that doubles your risk of developing depression, even if you have had no psychiatric history. So there are a lot of relationships,” Dr. Sethi said.
What research says?
A 2021 Stanford study has linked insulin resistance to an increased risk of developing major depressive disorder. “It’s been shown that about 40% of patients suffering from mood disorders are insulin-resistant,” Natalie Rasgon, MD, PhD, professor of psychiatry and behavioral sciences, said. The study is published online in the American Journal of Psychiatry.The scientists at Stanford analyzed 601 men and women (control group for the Netherlands study), who had no history of depression or anxiety at enrollment, and their average age was 41 years. They measured the three proxies of insulin resistance: fasting blood glucose levels, waist circumference, and the ratio of circulating triglyceride levels to high-density lipoprotein (HDL), the good cholesterol.They probed the data to see if the subjects found to be insulin-resistant had a heightened nine-year risk of developing major depressive disorder. By all three measures, the answer was yes: They discovered that a moderate increase in insulin resistance, as measured by the triglyceride-to-HDL ratio, was linked to an 89% increase in the rate of new cases of major depressive disorder. Similarly, every 5-centimeter increase in abdominal fat was related to an 11% higher rate of depression, and an increase in fasting plasma glucose of 18 milligrams per deciliter of blood was associated with a 37% higher rate of depression.The researchers found that insulin resistance is a strong risk factor for serious problems, including not only Type 2 diabetes, but also depression. “It’s time for providers to consider the metabolic status of those suffering from mood disorders and vice versa, by assessing mood in patients with metabolic diseases such as obesity and hypertension. To prevent depression, physicians should be checking their patients’ insulin sensitivity. These tests are readily available in labs around the world, and they’re not expensive. In the end, we can mitigate the development of lifelong debilitating diseases,” Rasgon added.
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