shows that DNA methylation by overall quartiles of the distribution differed by race/ethnicity recorded in the birth record (38% of blacks, 21% of whites, and 13% of Hispanics were in the highest quartile of DPM/μg DNA (indicating less DNA methylation) compared with 9% of blacks, 34% of whites, and 38% of Hispanics in the lowest quartile p=0.08). These racial differences are further highlighted in with DNA methylation levels cut at the overall median (66% of blacks, 48% of whites, and 29% of Hispanics are above the median DPM/μg DNA compared to 24% of blacks, 52% of whites, and 71% of Hispanics below the median, p = 0.03).
DNA methylation (DPM/μg) by race, New York Women’s Birth Cohort (Higher values indicate less DNA methylation).
The univariable associations between DNA methylation (log DPM/μg DNA) and lifecourse exposure variables are reported in . Compared to whites, blacks had higher log DPM/μg DNA (beta = 0.17, 95% CI = −0.11,0.44), although this result was not statistically significant when DNA methylation was considered as a continuous variable. Current smoking was positively associated, and prenatal smoke exposure was negatively associated, with log DPM/μg DNA, although these associations were not statistically significant. Birth length was associated with lower log DPM/μg DNA, indicating that longer babies had higher levels of DNA methylation (beta = −0.05 per cm, 95% CI = −0.10,−0.002). Later age at first birth was associated with lower DPM/μg DNA, indicating that older mothers had higher levels of DNA methylation (beta = −0.02 per year, 95% CI = −0.04,−0.004).
Unadjusted differences and 95% confidence intervals for the association between DNA methylation by prenatal, early life, adolescent and adult variables (Higher values indicate less DNA methylation).
reports the multivariable linear models (Models 1 and 2) of lifecourse variables and log DPM/μg DNA. Associations between race and DNA methylation did not decrease after further adjusting for lifecourse variables, suggesting that these selected variables did not explain the racial patterns in DNA methylation. Prenatal tobacco smoke exposure (beta= −0.34, 95% CI = −0.65, −0.02) and increasing birth length (beta= −0.11, 95% CI = −0.19, −0.02 per cm of length) were both associated with lower log DPM/μg DNA. In contrast birth weight was positively, but not statistically significantly, associated with log DPM/μg DNA (for comparison, the last column of reports standardized effect estimates). Both childhood smoke exposure and current smoke exposure were associated, but not significantly, with higher log DPM/μg DNA. These associations changed little when further adjusting for other variables that were statistically significantly associated with log DPM/μg DNA : later age at menarche (beta= −0.07, 95% CI = −0.13, −0.004), nulliparity (beta= −0.30, 95% CI = −0.57, −0.02) and age at first birth (beta= −0.03, 95% CI = −0.06, −0.01). These results did not change materially when adjusting for SES at age 7 instead of SES at birth. They also did not change when using self-reported adult race instead of race from the birth record.
Multivariable linear regression of DNA methylation (log DPM/μg) by prenatal, early life, adolescent and adult variables.