US researchers found that treating depression may protect against insulin resistance observed in depression in patients at risk of type 2 diabetes.

The study was conducted by Dr Julie Wagner of the University of Connecticut Health Center, and colleagues, and was presented at the 69th Scientific Sessions of the American Diabetes Association that took place in New Orleans, Louisiana from 5 to 9 June.

The researchers already knew from other recent studies that there was a link between depression and insulin resistance but the extent to which treatment for depression in adults at risk of type 2 diabetes affected insulin sensitivity was somewhat of a mystery so they decided to investigate.

Insulin resistance is where the body makes insulin, but can’t use it properly. Insulin is the natural chemical that helps us use glucose for energy.

The muscle, fat and liver cells of an insulin-resistant person don’t respond to insulin as well as they should so their pancreas makes more and more and eventually can’t keep up with the demand. This leads to excess glucose in the bloodstream, and prediabetes.

Many people with insulin resistance have both high insulin and high glucose levels in their blood at the same time.

For this study the researchers enrolled 55 patients who were on a diabetic prevention program. Each participant’s insulin sensitivity was calculated using the whole body method and their physical activity was assessed using the PA subscale of the Health Promoting Lifestyle Profile (which gives a score of 1 to 4).

Depression was measured using the Centers for Epidemiologic Studies Depression Scale (CESD) where a score of 16 and above indicated depression, and depression medication was assessed from self-reports and chart review.

The participants, who on average were 46 years old and obese, were mostly white (53 per cent) and female (90 per cent). 34 per cent had impaired fasting glucose and 28 per cent had impaired glucose tolerance.

They were categorized into three groups: (1) non-depressed (CESD score under 16, and not using anti-depressants), (2) treated for depression (on antidepressants regardless of CESD score), or (3) untreated depression (CESD score of 16 or higher, and not taking antidepressants).

The results showed that:

  • 33 per cent of the participants were depressed and 19 per cent were taking antidepressants (of these 46 per cent scored over 16 on the CESD scale).

  • As CESD score went up, physical activity and insulin sensitivity went down (they were inversely correlated).

  • Analysis of variance showed that those in the untreated depression group had significantly lower insulin sensitivity than those in the non-depressed group.

  • Those in the treated for depression group had similar insulin sensitivity to those in the non-depressed group.

  • These links were unaffected when physical activity was taken into account in the analysis of covariance.

The authors concluded that the results suggest:

“Treatment for depression in adults at risk for T2DM [type 2 diabetes mellitus] may improve the insulin resistance observed in depression.”

Wagner said in an interview with WebMD that:

“Insulin resistance is the hallmark of type 2 diabetes, and this study shows that treating depression is associated with improved insulin resistance.”

“Basically the depressed people on medication looked like the non-depressed people in terms of insulin sensitivity,” she added.

However, the authors cautioned that more research is needed before we can confidently say that treating depression delays or decreases the risk of type 2 diabetes.

Some experts suggest that depression may contribute to type 2 diabetes through the action of the stress hormone cortisol which plays a key role in the metabolism of sugar and fine tuning sensitivity to insulin. High levels of cortisol are also linked to belly fat, which is a risk factor for type 2 diabetes.

As Wagner explained to WebMD, the idea is that the more depressed a person is, the more cortisol their body makes, and this leads to more belly fat, higher risk of diabetes, and so a vicious cycle is set up.

Another theory is that depression disrupts the immune system and levels of the mood-regulating brain chemical serotonin which also helps to control metabolism.

“Depression, Depression Treatment and Insulin Sensitivity in Adults at Risk for Type 2 Diabetes.”
Julie Wagner et al.
Abstract 1850-P , Poster Session 1, 69th Scientific Sessions of the American Diabetes Association, June 2009.

Sources: American Diabetes Association, WebMD, National Diabetes Information Clearing House (NDIC).

Written by: Catharine Paddock, PhD