Turns out, there is an increasing need to prevent obesity because of the consequences for mental and physical health. The study explored the impact of aspects of physical health, such as body weight, heart health and blood pressure, to see whether a wide age range of individuals with poorer physical health went on to be less happy and less satisfied with their lives.
Previous studies have shown that individuals who are happier and more satisfied with their lives tend to have better physical health and live longer than those who have lower mental well being. But these studies leave the classic chicken and egg question – which comes first?
Using a technique called Mendelian randomization, the researchers asked whether poorer physical health causes lower mental well-being, or whether individuals with lower mental well-being are more likely to go on to have later problems with their physical health.
This technique provides evidence of the direction of causation by using genetic variants that have been associated with physical health and mental well-being. Unlike previous methods, this technique helps to rule out the influence of other factors that might be causing both physical health and mental well-being.
The research team was able to test 11 measures of physical health including coronary artery disease, heart attack, cholesterol, blood pressure, body fat and Body Mass Index (BMI).
Results suggested a consistent causal effect of higher BMI on lower mental well-being. There was little evidence that the other physical health traits were leading to less happiness and life satisfaction.
The same pattern of results was seen in a follow-up analysis using the UK Biobank cohort of over 300,000 individuals aged 40 to 70 years old. Here the authors were able to look at different aspects of life satisfaction and found that the key impact of higher BMI was on lower satisfaction with health. They were also able to show that the effect is present from age 40 through to age 70, and in both men and women.