Taking Birth Control Pills May Place Diabetic Women At Risk for Kidney Disease

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Oral contraceptives, angiotensin-dependent renal vasoconstriction, and risk of diabetic nephropathy, by S.B. Ahmed and colleagues. Diabetes Care 28:1988–1994, 2005.

What is the problem and what is known about it so far?

Previous studies have shown that taking birth control pills affects the body's system to regulate blood volume and blood pressure. When this system is triggered, it affects blood flow in the kidneys and the kidneys' ability to filter out waste products, possibly leading to kidney disease over the long-term. Diabetes is the leading cause of fatal kidney disease in the U.S., but there have only been a few studies that have looked at the effects of taking birth control pills on kidney function in women with diabetes.

Why did the researchers do this particular study?

The researchers conducted two studies to look at how birth control pills affect kidney function in women with diabetes.

Who was studied?

In their first study, the researchers examined 92 women: 12 women with diabetes who were taking birth control pills, 10 women who did not have diabetes and were taking birth control pills, 29 women with diabetes who were not taking birth control pills, and 41 women who did not have diabetes and were not taking birth control pills.

In their second study, the researchers examined 114 women who were recently diagnosed with type 1 diabetes. Thirty-three of these women were taking birth control pills.

How was the study done?

In the first study, the women were given captopril, a pill to treat blood pressure, to see how it affected the blood flow in the kidneys. If blood flow increased in the kidneys after taking the blood pressure medicine, then it would be a sign that before taking the medication, the body's system to regulate blood flow and blood pressure was triggered, which puts more pressure on the kidneys.

In the second study, the researchers looked at the direct effect of birth control pills on the health of the kidneys. They examined data that covered a period of almost 21 years.

What did the researchers find?

In the first study, the women who did not have diabetes and were not taking birth control pills had only a slight increase in kidney blood flow after taking the blood pressure medicine. The women who did not have diabetes and were taking birth control pills had a much greater increase in kidney blood flow. The women who had diabetes but were not taking birth control pills also had a greater increase. And the biggest increase was seen in women who had diabetes and were taking birth control pills.

The results of the second study showed that 18% of the women who took birth control pills eventually got macroalbuminuria, which is when the kidneys do not properly filter out waste products and is a sign of kidney damage. Only 2% of the women who were not taking birth control pills got this condition.

What were the limitations of the study?

In the first study, the researchers did not record the menstrual cycles of the patients. The menstrual cycle has been shown to affect the system that controls blood pressure and blood flow. The first study included women with who had type 1 or type 2 diabetes, while the second study focused only on women with type 1 diabetes. In both studies, women who took birth control pills were younger than women who did not take birth control. The studies did not take into account whether the women smoked; smoking of course affects blood pressure and blood flow. And the number of women included in each study was relatively small.

What are the implications of the study?

The use of birth control pills appears to put women with diabetes at risk for kidney disease, although larger studies are needed to fully examine the effects of taking birth control pills on kidney function. Physicians should remain cautious about prescribing birth control pills to women with diabetes.

For more information

Preconception care of women with diabetes, by the American Diabetes Association. Diabetes Care 26 (Suppl. 1):S91–S93, 2003.

Diabetes and Nephropathy (Kidney Complications)

Kidney Disease

Hormonal birth control: a gestational diabetes risk? by T. Kordella. Diabetes Forecast, February 2005