Do the long nights and shoddy weather over the winter months make you feel low? If so, you could also be at raised risk of cardiovascular disease and being overweight, according to new research in PLoS ONE.
This study of 11,545 Norwegian adults found that people who were classified as having considerable variations in mood across the seasons had a higher BMI and waist to hip ratio, and higher levels of fat in their blood, than people who were less affected by the seasons.
In addition, women who had “high seasonality” tended to do less exercise and were more likely to smoke daily than their “low seasonality” counterparts. All these factors add up to an elevated risk of cardiovascular disease, according to the study authors.
The most well known variant of seasonal mood changes is seasonal affective disorder (SAD), which is characterised by severe episodes of depression that only occur during a particular time of year. SAD affects an estimated 7% of the UK population every winter between September and April, in particular during December, January, and February. Seasonality is distinguished by milder variations in mood rather than major lows, although high seasonality combined with a propensity for depression is thought to be a risk factor for SAD.
People with SAD or high seasonality tend to eat more, gain weight, and feel more sleepy during episodes. This could be advantageous from an evolutionary point of view, because it could facilitate energy storage and promote reproductive potential in the seasons optimal for conception, gestation, and lactation. In the modern world, however, we have access to resources all year round and don’t have to worry about energy storage, so seasonality may conversely be a stress factor.
In the new PLoS ONE study, all individuals in Hordaland county, Norway, born between 1953 and 1957 (i.e. aged 40–45 years) were invited to participate, 63% of whom said yes. These 8,598 men and 9,983 women filled in questionnaires about their seasonal fluctuations in mood and behaviour and about their health behaviours. Blood samples were taken and height, weight, waist circumference, hip circumference, and blood pressure were measured.
In both men and women, weight, BMI, waist-hip ratio, and blood levels of triglycerides increased as the level of seasonality increased. For example, the average BMI for men with low seasonality was 25.9, a touch overweight but otherwise fine, but for men with high seasonality to the point of having SAD the average BMI was 27.1, definitely overweight.
Women with high seasonality were about 20% less likely to do at least three hours of exercise a week than their less affected counterparts, and tended to drink and smoke more. Furthermore, the association between seasonality and BMI in women was affected by when the researchers took their measurements: BMI increased over autumn and winter in women with high seasonality.
Given the high BMI, weight, and blood fat levels in people with high seasonality, the authors state that “Overall it seems to be fair to conclude that subjects with high seasonality have an elevated risk for cardiovascular disease.” They do point out that a cross-sectional study such as theirs can’t pinpoint causation though: we don’t know whether high seasonality causes poor health or whether poor health is responsible for high seasonality.
Øyane N et al. (2010) Increased Health Risk in Subjects with High Self-Reported Seasonality. PLoS ONE 5 (3). DOI: 10.1371/journal.pone.0009498