The investigators measured IgG antibodies specific to C. pneumoniae (not to be confused with Chlamydia trachomatis, the STD) in a cohort of 5,044 men and women born in Northern Finland in 1966. They looked at the relationship between positive IgG titers and body mass index, waist-to-hip ratio, and waist & hip circumference. They also measured C-reactive protein (hsCRP) to assess chronic inflammation as a contributor to obesity.
The presence of C. pneumoniae IgG antibodies, alone and with elevated CRP, correlated firmly and independently with elevated BMI for women and men. Women, but not men, also showed correlations between C. pneumoniae exposure and high waist and hip circumference. The findings were published in the December 2011 edition of the International Journal of Obesity.
This is not the first time C. pneumoniae has been linked to obesity; other viral and bacterial pathogens including Helicobacter pylori have also been associated with weight gain. Chronic inflammation triggered by these pathogens may be the key factor.