Excessive weight can cause depression, say researchers, with effects that they thought were mostly psychological.
Although previous studies have found that people with obesity greater chances of having depression, it was unclear whether it was all over to depression leading to a change in weight or turnaround.
Now, in the largest study of this type, experts say genetic variations associated with body mass index (BMI) can lead to depression, with a stronger effect in women than men. Moreover, they say that research suggests that the effect can be reduced to factors such as body image.
"People who are predominant in the population are more depressed, and this will probably be at least partially [a] causative effect BMI [on] depression, "said Professor Tim Frailing, a co-author of the study at the University of Medicine in Eketer.
Researchers from Great Britain and Australia wrote in the International Epidemiology Journal on using data from UK Biobank, a research work involving 500,000 participants aged 37 to 73 who were recruited in the period 2006-10.
The researchers reviewed 73 genetic variants associated with high BMI that are also associated with a higher risk of illness such as diabetes and heart disease. They also examined 14 genetic variants associated with a high percentage of fat in the body, but which were associated with a lower risk of such health problems.
The team then reviewed the patient's hospital information and answers from a number of questionnaires – including the self-report on visiting a GP or psychiatrist for anxiety or depression. The team identified about 49,000 participants who were relieved of depression.
Overall, the team found that people with a higher ITM are probably more depressing.
The researchers also found that genetically predisposed to higher BMI was associated with depression, with a stronger effect in women than in men. The results were sustained even when they performed additional tests, such as excluding individuals with family history of depression and when the analysis was repeated on data from a major international project called Psychiatric Genomic Consortium.
Focusing on 73 genetic variants and taking into account factors involving age and sex, found that for each increase in BMI of 4.7 points, chances for depression increased by 18% overall and by 23% in women.
When the team combined data from different sources, they found 14 genetic variants that increase body fat, but are not associated with metabolic patients, are also associated with an increased chance of having depression.
"It suggests that the psychological component is as strong as any physiological component, if [the latter] there is a general, "said Frailing, pointing out that a bad body image could be one mechanism in the game.
The study has certain limitations: it primarily concerned individuals with a white European origin and included some self-esteem data.
Although the study does not show that weight gain for other reasons increases the risk of depression, Frailing said it is likely. "Allows [one] to conclude that greater effects in BMI will have a greater impact on depression, "he said.
Naveed Sattar, professor of metabolic medicine at the University of Glasgow, welcomed the research. "These new findings are probably the strongest so far to suggest greater weight that can contribute to depression," he said. "Of course, many other factors can cause depression, but even so, weight loss can be helpful in improving mental health in some individuals, while maintaining a lens at all should help reduce the chances of depression."