This is the 50th anniversary of the birth control pill; a tiny thing that has revolutionized society. Taking the pill does tend to increase blood glucose levels so it might be useful to consider the ramifications of using this pregnancy avoidance tool while managing one’s diabetes. The pill essentially consists of some combination of the hormones estrogen and progesterone. These hormones provide important instructions to reproductive tissues in a carefully timed fashion. Birth control pills create a hormonal state that makes the body think it is already pregnant and blocks any new eggs developing. Thus actual pregnancy is avoided.
Probably the first thing you have focused on is this increase in blood glucose. How much are we talking about? Actually – not much. The amount of increase in non-diabetic women is considered by the American Diabetes Association not enough to be concerned about. For women with diabetes, however, the debate is spirited. One school of thought is that any increase in blood sugar is an increase in risk and should be concerning. The other school of thought, of course, is that the benefits of avoiding an unwanted pregnancy outweigh the minimal risk.
We have known for quite some time that birth control pills decrease insulin sensitivity and this is caused entirely by progesterone. The mechanism appears to be complicated in that progesterone seems to act at multiple levels in the insulin signaling pathway. Interestingly, the progesterone receptor, upon binding progesterone, travels to the nucleus of the cell and regulates the expression of numerous genes. Several of these genes target the insulin signaling pathway in a variety of ways suggesting that this is a very deliberate piece of evolutionary integration.
About a decade ago, a progesterone only pill was developed in response to potential cancer risks associated with estrogen. This has proved useful for women with diabetes as well since estrogen increases the rate of developing a type of diabetic complication known as macrovascular disease (heart attacks would be one example). Indeed the American College of Obstetricians and Gynecologists recommend that women who are diabetic and either over the age of 35 or have vascular disease should use a progesterone-only contraceptive. Interestingly, in epidemiological studies of diabetes incidence it was noted that there has been an increase in the number of cases of adolescent girls developing type 2 diabetes. The beginning of this increase corresponded suspiciously with the time at which the progesterone only pill was introduced, leading researchers to question whether or not there might be a connection.
In a large meta-analysis of the literature, a group found no evidence for any general increase in diabetes risk for non-diabetic women taking hormonal birth control pills. They mentioned, however, that the available studies were small and often poorly controlled. Indeed it seems as if this is an area of study that has been neglected. However, in a review of the literature focusing on injectable and implantable forms of hormonal therapy, I did find something interesting. In 2001 a group published a study of Navaho women using birth control. They compared women who used a progesterone only implant to those who used a combination progesterone/estrogen formulation. There was a clear increase in diabetes incidence for the women who used a progesterone only implant. Now there are two potentially important factors to consider here. First of all, Native Americans are much more prone to diabetes than Caucasians or the other races of human with whom we share this place. This may be due to different genetics, a different lifestyle of some combination of the two. The second important factor is that these women were quite overweight. We do not yet have a clear sense of the importance of this factor however it is likely that obesity places an increased stress on the insulin system and one can imagine that the very small stress of progesterone might have a greater consequence in this population.
Given the fattening of America, it would be a good thing for us to examine this issue a bit more carefully.