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Is there a link between obesity and mental health?

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Adiposity, the state of being obese, is associated with poor mental health in middle age only according to the latest research led by Professor Meena Kumari with Professor Michaela Benzeval and Apostolos Davillas at the Institute for Social and Economic Research at the University of Essex using data from Understanding Society, the UK Household Longitudinal Study.

Researchers studied a group of 11,257 participants. Each person was given a medical examination where their weight, height, waist circumference and percentage fat were measured to assess a number of measures of adiposity. Body mass index was calculated from height and weight. They also completed a General Health questionnaire to check for symptoms of depression and anxiety and the mental component summary to assess mental health functioning. The findings are published in the February issue of Plos One.

The researchers found that greater adiposity was associated poorer mental health functioning but not in all age groups. The association of greater adiposity and poor mental health functioning was seen in those aged in their 30s to 50s and then decreased in older ages. Diseases such as cardiovascular disease, arthritis and endocrine diseases played a role in explaining the association of body mass index with mental health functioning. The association of waist circumference and mental health functioning remained associated with each other in middle age after taking into account a wide variety of factors.

Several explanations were suggested by the researchers for their findings. First, social isolation potentially experienced by people who are obese may be greater at younger than older ages. Secondly, increased adiposity may be considered normative in older age groups and thus, may be less associated with poor mental health than in younger age group. Thirdly, people who have large waists, that is, are ‘apple-shaped’ may have a poor self-body image and therefore be at greater risk of developing poor mental health functioning.

Professor Kumari said: “This study emphasises the inter-relatedness of obesity, diseases and mental health and suggests that treatment of any of these problems in isolation may be less beneficial than addressing them in combination.”

“The research is useful because there has been a massive increase in adiposity levels in the population recently - at the same time mental health is thought to have deteriorated, on average in the population and it is useful to understand how adiposity and mental health are related.

I think in layman’s terms, the general perception is that increased adiposity (greater body mass index, having a bigger waist or higher percentage fat) would be associated with poorer mental health. However, the papers that have looked at the question don’t always see this, some evidence shows that increased weight is actually associated with better mental health (this is called the ‘jolly-fat’ hypothesis) but there are papers that show that increased adiposity is associated with poor mental health functioning.

We wondered if these findings were mixed because researchers have varied in what they include in their analyses to try and explain their associations or that the associations might be different in different age groups. Understanding Society is a good study to try and examine this association because it has measured height, weight and other measures of adiposity by a nurse (rather than just asking people) and we have lots of variables collected to help us understand any associations that we might see. Most importantly, unlike a lot of other studies, we have adults right across the adult age range.

We didn’t see an association of adiposity and mental health functioning in young (under 30) or older people (over 50). The associations we see are restricted to the ‘middle aged’, which might explain why the literature is mixed. Further, in middle age having a chronic disease (cardiovascular disease, arthritis and endocrine disease) appeared to account for the association of BMI and mental health functioning. It might be because people with disease develop poor mental health and obesity or that obesity causes poor mental health and disease or that poor mental health causes disease and obesity - we don’t know from these analyses but we concluded that clinicians should think about how these things are inter-related as each one is important in middle age.”

Read the full paper: Association of Adiposity and Mental Health Functioning across the Lifespan: Findings from Understanding Society (The UK Household Longitudinal Study)

Photo credit: Anthony Cullen for Understanding Society