COLORADO SPRINGS — Large body size in youth is associated with increased risk of atrial fibrillation in later life among men, Dr. Annika Rosengren said at a conference sponsored by the American Heart Association.
“If you were tall, or had a lot of muscles—if you were a big man—you had more risk of atrial fibrillation. And you could add to this risk further by putting on weight after age 20,” according to Dr. Rosengren, professor of medicine at Sahlgrenska University Hospital, Goteborg, Sweden.
The implication of this novel finding from a large Swedish longitudinal study is that the already-high prevalence of atrial fibrillation (AF) in Western societies is going to keep climbing, and the increase won't simply be due to the graying of the population, high rate of inadequately controlled hypertension, and worsening obesity epidemic, all of which are well-recognized contributors to AF.
Size is an additional, widely unappreciated contributor to AF risk, she said in an interview: “Each successive generation is bigger in youth. People are not only growing fatter with each succeeding cohort being born, they're also getting taller and larger, independent of obesity. So expect more atrial fibrillation.”
She reported on 6,903 Swedish men who were a mean of 52 years old in the early 1970s when they enrolled in the Swedish Primary Prevention Study. They were then followed until 2004, for a maximum of 34 years.
During follow-up, 18% of the men were diagnosed with AF.
The participants' body surface area at age 20 proved strongly related to subsequent risk of AF, based on a Cox regression analysis adjusted for midlife body mass index and other potential confounders. Of note, the men turned 20 during 1935–1945, a period when “obesity was virtually nonexistent in Sweden,” Dr. Rosengren observed.
In the adjusted regression analysis, men in the second quartile of body surface area at age 20 had a 42% greater risk of later developing AF as did men in the lowest quartile. Men in the third quartile had a 58% increase in risk, while those in the top quartile for body surface had a 200% greater risk. Body weight at age 20 showed a virtually identical association with subsequent AF.
“The mechanism is probably that if you're big, whatever the cause, there's a high likelihood of having large atria—and large atria are more prone to develop atrial fibrillation,” the physician explained.
In nature, AF doesn't occur in small species of animals but is common in giraffes and other large creatures, she added.
Weight gain between age 20 and midlife was also independently associated with increased AF risk in the Swedish men.
A 5%–15% bump in body weight over the decades was associated with a 13% greater rate of AF, compared with no change in weight. A 16%–35% weight gain was associated with a 33% increase in AF rate, while a more than 35% increase in weight was followed by a 61% increase in risk.