A new Brigham Young University study found that parenthood is associated with lower blood pressure, particularly so among women. ... The study involved 198 adults who wore portable blood pressure monitors, mostly concealed by their clothes, for 24 hours. The monitors took measurements at random intervals throughout the day -- even while participants slept. This method provides a better sense of a person's true day-to-day blood pressure. Readings taken in a lab can be inflated by people who get the jitters in clinical settings. It's a real phenomenon known as the "white coat" effect, and it can mess up the results of studies done without the portable monitors. A statistical analysis allowed the researchers to account for other factors known to influence blood pressure -- things like age, body mass, gender, exercise, employment and smoking -- and zero in on the effect of parenthood. For parents overall, the 24-hour blood pressure readings averaged 116 / 71. All other things being equal, parents scored 4.5 points lower than non-parents in systolic blood pressure (the top number) and 3 points lower than non-parents in diastolic blood pressure. Holt-Lunstad says the size of the difference is statistically significant, but she warns against hastily making major life changes based on this finding alone.
This finding is interesting because it seems to go against our expectations. I assume that there's no real direct physiological process at work here; e.g., hormone changes due to pregnancy or lactation reducing blood pressure. Rather, it is likely that the choices one makes in life are strongly shaped by having children, and those choices somehow modify health outcomes in ways we don't have a good grasp of yet. The researchers controlled for the variables which they knew about, but there are surely many hidden ones which are the real causes of the effect seen here. Pretty typical correlational study, novel for the against-expectations sign of the value. Also, I do think it's a little amusing that the work comes out of Brigham Young University. Presumably the authors know a lot about the pro-natalist lifestyle from personal experience. And Mormon "clean living" has resulted in lower morbidity and higher life expectancy from what I have heard.