According to Dr. Alison M. Stuebe of Brigham and Women's Hospital and Harvard Medical School in Boston, she and her colleagues were prompted to examine the issue as various studies have suggested that breastfeeding affects women's metabolism and that metabolism, lactation, and reproduction are all linked.

In order to find any association between lactation duration and the development of type 2 diabetes, Stuebe and her colleagues analyzed data from two large groups of women who had given birth.

The first group included 83,585 women who were part of the Nurses' Health Study, and the second group included 73,418 women who were part of the Nurses' Health Study II.

The second group is apparently a younger group.

The researchers found that in the first 15 years after a woman's last delivery, each year of breastfeeding was associated with a 15-percent reduction in her risk of diabetes.

The analysis took into account diet, exercise, smoking status, whether or not the women took multivitamins, which is an indicator of whether women are health-conscious, and they still found a 15-percent benefit.

Stuebe says that beyond 15 years after the last birth there was less of a benefit, but for at least the first 15 years there seems to be some long-term association that protects women from diabetes.

She explains that pregnancy in some respects is a pro-diabetic state as the mother has more resistance to insulin, which is the way the body makes sure that the fetus acquires enough sugar.

Then lactation begins which to some extent is an anti-diabetic state.

The researchers' theorise that lactation resets the body after pregnancy and if a woman does not breastfeed for a prolonged period of time, the risk of diabetes might increase.

Stuebe says the findings provide more reasons to encourage women to breastfeed as it is good for babies and for mothers.

The research is published in the current edition Journal of the American Medical Association.

"We were not able to show any relationship between the genetic variations and benefits associated with diuretic therapy," Johnson said. "Thus, our data suggest that we would not use this genetic information to help determine who should get a diuretic. However, it does provide us clues into at least one gene that likely places people at risk for death, heart attack and stroke, and so perhaps in the future this information can be used to be more aggressive in the preventive therapies for these individuals."

As researchers learn more, they hope to better understand the complex interplay between genes, disease development and the treatments that work best depending on one's DNA. For now, identifying patients at risk remains a challenge, and treatment is often inadequate, Johnson said.

"There are five first-line drug classes, with probably an average of seven to eight drugs in each class, then an additional half-dozen or so other drug classes that aren't considered first-line," Johnson said. "This means there are many choices for drug therapy in hypertension - a good thing - but also adds to the trial-and-error element of finding the right drug for the right person, as any specific drug has only about a 50 percent chance of being effective in a specific patient."

Identifying genetic risk factors is only the first step, said epidemiologist Sharon Kardia, Ph.D., director of the Public Health Genetics Program at the University of Michigan School of Public Health.

"Large research studies need to be undertaken to prove that genetic risk can be reduced through medical or public health interventions. Second, this whole new realm of genomic medicine greatly expands the responsibilities of doctors, nurses and pharmacist to assure the proper use of genetic information in prescribing, dispensing and administering drug therapies," Kardia said. "Lastly, we have to tread lightly until we have assurances that people's genetic information will be properly protected so that identifying someone as more expensive or difficult to treat won't result in insurance or perhaps job discrimination. As Dr. Johnson's research illustrates, we now have good evidence that we should be investing in genetics education, regulation and social engagement so that we can move these results to the next level - namely, decreasing health-care costs and saving lives."

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