Greater Birth Length Increases Vulnerability to Breast Cancer
Reinforcing the connection between breast cancer and birth size, birth length is also associated with an elevated risk for this disease. One Norwegian study determined that for women under the age of 50, those who were equal to or longer than 53 centimeters (21 inches) at birth had a 1.5 times greater risk of developing breast cancer when compared to women who were 50 centimeters (19.5 inches) or less. This correlates nicely with data that has shown taller adults are more prone to develop breast cancer. Again, greater fetus and baby size seems to lead to greater concentrations of estrogen and other hormones being present, and estrogen is notorious for its capacity to increase breast cancer risk generally.
One incongruity in the connection between height and breast cancer is the fact that greater height in adult women is usually associated with late-onset menstruation, while it is well known that early-onset menstruation can be a significant breast cancer risk factor. Because length at birth is considered a good predictor of height later in life, this seeming inconsistency is likely related to complexity in human growth patterns or perhaps to the way risk factors may offset more favorable characteristics.
The Length of Gestation and Breast Cancer
Longer than normal gestation periods are known to be a risk for breast cancer, presumably because of longer fetal exposure to estrogen and/or other chemicals associated with breast cancer risk. However, a shorter than normal gestation period has also been shown to elevate breast cancer risk. A Swedish study, for example, found that women who were born prematurely, at 33 weeks or less, were four times more likely to develop breast cancer later in life. Shorter pregnancies in many instances are marked by the presence of greater concentrations of female hormones, and this seems to be the relevant factor more so in some cases than length of time spent in utero. Whether this greater concentration of female hormones is actually causing early birth, or is just a symptom of some deeper-lying process controlling birth is unknown.
The Mysteries that Remain
These kinds of studies, and some of the contradictions and seeming inconsistencies they reveal, shows how complex the question of what ultimately causes breast cancer really is. One thing that should be pointed out is that while most scientific attempts to explain pre-birth risk factors focus primarily on fetal exposure to estrogen and other female sex hormones, this is really a theory based on extrapolation rather than an established fact. Biology, environment, and lifestyle certainly all play a role in the development of breast cancer, but there is still much to study and learn about the way positive and negative risk factors cancel out or reinforce each other in individual cases.
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