Obesity is an independent risk factor for depression

Summary: Metabolic disorders and depression are widespread. It is a well-established fact that obesity increases the risk of metabolic diseases like diabetes or cardiovascular conditions. Further, studies show that obesity also considerably increases the risk of depression. Although the relationship between obesity and metabolic disorders is quite clear, researchers are not sure how it increases the risk of depression. The new study, one of the biggest of its kind, analyzed data of 145 669 subjects. It divided subjects into two groups, one with a favorable metabolic profile and another unfavorable one. And the study found that the risk of depression was equal in both groups, and it increased in proportion to an increase in BMI. Thus, the study concluded that higher depression in obese individuals has a greater association with social factors than physical factors.

 Obesity and associated health conditions and mental disorders are now the leading causes of morbidity and disability among men and women. What is even worrisome is that both obesity and depression are on the rise. These conditions are increasingly affecting younger adults.

In the US, more than 40% of adults are obese with a BMI of above 30. Additionally, another 30% are overweight with BMI above 25. Studies show that those living with obesity are more likely to develop diabetes, joint disorders, and other physical illnesses. At the same time, data shows a greater prevalence of depression among people living with obesity¹.

Figure 1 obesity increases the risk of depression

The relationship between obesity and physical diseases like diabetes or heart diseases is reasonably well understood. However, very little is known about what increases the risk of depression in obese individuals. For example, is this higher rate of depression secondary to health conditions like diabetes, hypertension, heart disease, or is it due to factors like social stigma related to obesity?

To understand what increases the risk of depression in obesity, researchers did one of the most extensive studies to date. They analyzed the data of 145 669 European participants using Mendelian randomization (MR). These all participants were obese but belonged to two different genetic groups².

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One group consisted of obese adults that carried a gene that makes them less prone to obesity-related metabolic disorders. Thus, although these individuals were obese, they were metabolically quite healthy.

Another group was made of individuals who were obese and genetically prone to various metabolic disorders. Thus, they were not only obese but had various metabolic diseases.

To the amazement of researchers, both the groups had an almost equal prevalence of depression and other mood disorders. They also found that the risk of depression had a direct relationship to BMI. Higher BMI in both groups was associated with a higher prevalence of depression.

As the study had a large sample size, it clearly indicates that higher BMI is an independent risk factor for depression in obese individuals. It means that the presence of other metabolic disorders, which are often secondary to obesity, are minor contributors to the risk of depression.

In practice, it means that those with obesity have a higher risk of developing depression, and this risk keeps on increasing with an increase in BMI. Depression is equally common among metabolically healthy obese adults and metabolically less healthy adults. Thus, managing obesity would considerably reduce the risk of depression and other mood-related disorders.

It also appears to show that psychological factors might be playing a more significant role in the development of depression in obese adults. In comparison, metabolic changes caused by obesity have a lesser role in the development of depression in such people.

This study also noticed that although high BMI is associated with a greater risk of depression. But high BMI does not appear to have a similar relationship with a generalized anxiety disorder (GAD).

However, the study has some limitations. Researchers noticed that although the prevalence of depression was equal in both groups, that is, people with a favorable and unfavorable metabolic profile. Nonetheless, even in those with favorable metabolic profiles, there were signs of inflammation like elevated C-reactive protein levels.

References

1. CDC. Obesity is a Common, Serious, and Costly Disease. Centers for Disease Control and Prevention. Published June 7, 2021. Accessed October 24, 2021. https://www.cdc.gov/obesity/data/adult.html
2. Casanova F, O’Loughlin J, Martin S, et al. Higher adiposity and mental health: causal inference using Mendelian randomization. Human Molecular Genetics. 2021;(ddab204). doi:10.1093/hmg/ddab204