SAD and Obesity: What's The Link

In a recent study, CAMH researchers examined the link between season of birth and body weight in women with Seasonal Affective Disorder (SAD).  Led by Dr. Robert Levitan and Dr. James Kennedy, the study examined whether the season a person was born in impacted body weight regulation in individuals with SAD.  Their investigation included possible interaction effects with the 7R allele (specific section of DNA coding) of the dopamine-4 receptor gene (DRD4), the gene that influences weight gain by causing loss of sensitivity to the brain chemical dopamine.

The study revealed that those women born in the spring and carrying the 7R allele (designated the high-risk group) had an average maximum Body Mass Index (BMI) 26% higher than those individuals born in other seasons and without the 7R allele (designated the low-risk group).

These investigators also looked at lifetime rates of obesity and morbid obesity in both the high-risk and low-risk groups.  The high-risk group was significantly more likely to experience obesity or morbid obesity. 53% of the high-risk group had obesity at some point in their lives, compared to 20% of the low-risk group.  Looking at morbid obesity, 24% of the high-risk group experienced this condition compared to just 4% in the low-risk group.

At a genetic level, these results expand our understanding of weight gain and obesity in women with SAD by suggesting that factors linked to birth season, such as early exposure to hormones tied to seasonal light/dark cycles, interact with the DRD4 gene to influence body weight regulation in this population.

Overall, these results also point to a novel interaction between a person’s genes and the environment during the early stages of brain development, which triggers weight gain and obesity later in life.  The authors propose that this phenomenon is the result of a seasonal thrifty phenotype, a historical behavioural strategy programmed in our genes that enhanced survival in northern latitudes.  Thousands of years ago, characteristics seen is SAD, such as increased eating and decreased activity, were adaptations to or predictors of seasonal famine in areas further from the equator.  However, in today’s environment of plentiful food, these characteristics create an increased risk for obesity in women with SAD.

Click A Birth-Season/DRD4 Gene Interaction Predicts Weight Gain and Obesity in Women with Seasonal Affective Disorder: A Seasonal Thrifty Phenotype Hypothesis for more information.

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