At first blush, this might seem like nothing more than a statistical oddity. However, it's not the only study to find a link between autumn birthdays and addiction, especially in males. For example, a national survey of nearly 43,000 Americans found that alcohol dependence was more common in men, but not women, who were born in autumn.
Now and Then
For men with autumn birthdays, a predisposition to nicotine addiction may be partly rooted in events that occurred before or soon after they were born. Several risk factors vary with the seasons, including sunlight, temperature, viral infections, and vitamin D (made by the body after exposure to the sun's rays).
In the case of nicotine addiction, one hypothesis is that the number of hours of daylight during or soon after pregnancy may affect developing neurotransmitter systems. Specifically, "there may be long-term effects on dopamine that extend into adulthood," says Kaisa Riala, MD, PhD, lead researcher on the Finnish study. Dopamine is a brain chemical that plays a key role in the craving for drugs. Nicotine, like other addictive drugs, floods the brain's reward circuits with dopamine. This is what makes taking a puff on a cigarette so rewarding for a smoker - and giving up that cigarette so difficult.
There's some evidence that birth season and dopamine may interact differently in men and women. In particular, both season of birth and gender may affect variants in the DRD4 gene, which encodes a type of dopamine receptor. This might explain the different seasonal pattern seen in males versus females.
Night and Day
What's the connection between a fetus's or newborn's developing dopamine system and the length of days? Researchers believe that it might have something to do with the delicate balance between dopamine, which helps signal the body when it's daytime, and the hormone melatonin, which helps signal the body when it's night. But there is still a lot that remains to be learned. At this point, any explanation is "quite hypothetical," Riala says.
Several genetic and environmental factors affect your risk of becoming addicted to nicotine. For example, you're more likely to smoke if you start young, have depression or another mental illness, or abuse alcohol or other drugs. For men, having a birthday in September, October, or November may be another risk factor to add to the list.
Read more about season-of-birth effects on health.
Linda Wasmer Andrews is a health writer with a master's degree in health psychology.
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