It found that breastfeeding for at least one month lowered the mother's risk for developing diabetes later in life, even after controlling for many confounding factors such as physical activity status, BMI, etc.
Interestingly, women who had given birth but not breastfed for at least a month were at greater risk for diabetes later on than women who had never given birth at all. That was a surprising finding.
According to a discussion of the study at the Breastfeeding Medicine blog:
The study included 2,233 women between the ages of 40 and 78 who were members of a large integrated health care delivery organization in California. Strikingly, one of every four mothers who had never breastfed had developed type 2 diabetes.
Mothers who had not breastfed were almost twice as likely to develop diabetes as women who had breastfed or women who had never given birth. These long-term differences were notable even after considering age, race, physical activity and other factors which affect risk of diabetes such as alcohol and tobacco use...
In other words, breastfeeding is part of the way mothers’ bodies recover from pregnancy. When this process is interupted, and an infant is fed something other than...mother’s milk, a mother’s body suffers.The authors did control for BMI and physical activity in the analysis, among other things. According to the study's abstract:
Multivariable logistic regression was used to control for age, parity, race, education, hysterectomy, physical activity, tobacco and alcohol use, family history of diabetes, and body mass index while examining the impact of duration, exclusivity, and consistency of lactation on risk of having developed type 2 diabetes.A couple of limitations of the study are its fairly small size --- 2233 women total, only 1828 of whom were mothers --- and its low threshold for length of breastfeeding (greater than or equal to 1 month of breastfeeding).
That means the study had only 1024 women who breastfed 1 month or longer, and while that's nothing to sneeze at, you really need a bigger data set, looking at a longer duration of breastfeeding, to prove population-wide effects most clearly.
Sadly, only 56% of the women in the study had breastfed their children for more than one month, another limitation of the study. This very low rate almost certainly reflects the age of the women in the study (40-78) and the active discouragement of breastfeeding many of the older women encountered.
Still, the study reports a striking finding and yet another reason to pursue breastfeeding.
It also points out what a disservice doctors did to women years ago when they actively discouraged breastfeeding, and the dangers of sweeping health policies that interfere with the way our bodies were designed to undergo pregnancy, birth, and postpartum.
Previous research on Breastfeeding and Later Diabetes
Some previous research has also tied length of breastfeeding to a lower risk for later diabetes in mothers.
A Chinese study (Villegas 2008) found that breastfeeding modestly lowered the risk for later diabetes in women followed for just under 5 years. They reported:
Women who had breastfed their children tended to have a lower risk of diabetes mellitus than those who had never breastfed [relative risk (RR)=0.88; 95% CI, 0.76-1.02; p=0.08]. Increasing duration of breast-feeding was associated with a reduced risk of type 2 diabetes mellitus. The fully adjusted RRs for lifetime breast-feeding duration were 1.00, 0.88, 0.89, 0.88, 0.75 and 0.68 (p trend=0.01) for 0, 0 to 0.99, 0.99 to 1.99, 1.99 to 2.99, 2.99 to 3.99, and greater than or = 4 years.One of the largest studies on breastfeeding and maternal diabetes was published in The Journal of the American Medical Assocation (Steube 2005). It used large datasets from the Nurses Health Study (121,700 women from 11 states) and the Nurses II Health Study (116,671 women from 14 states) to study the effect of lifetime duration of breastfeeding on later risk for diabetes. They found:
Among parous women, increasing duration of lactation was associated with a reduced risk of type 2 diabetes. For each additional year of lactation, women with a birth in the prior 15 years had a decrease in the risk of diabetes of 15% (95% confidence interval, 1%-27%) among NHS participants and of 14% (95% confidence interval, 7%-21%) among NHS II participants, controlling for current body mass index and other relevant risk factors for type 2 diabetes...
Longer duration of breastfeeding was associated with reduced incidence of type 2 diabetes in 2 large US cohorts of women. Lactation may reduce risk of type 2 diabetes in young and middle-aged women by improving glucose homeostasis.So there's a study with a very large dataset that found that breastfeeding -- the longer the better -- lowered the risk of mothers developing type 2 diabetes later on.
Keep in mind that this study also reflected our society's tendency towards short breastfeeding periods. They traced a woman's lifetime exposure to lactation (how long she breastfed all her children cumulatively), and their highest category was "greater than 23 months."
Greater than 23 months over your lifetime? Heck, I breastfed every single one of my kids at least that much each time, so how does that affect my risk for type 2 diabetes? My total lifetime exposure to lactation is right around 10 years. Does each additional cumulative year above 23 months help lower my risk that much more? The Chinese study cited above seems to suggest so, but its maximum lifetime exposure category was greater than or equal to 4 years.
I would love to seen the JAMA researchers collect information about a far greater lenth of total lactation in U.S. women than 23 months, but the fact is that our long-term breastfeeding rates in this country are so poor that they probably would have had trouble finding enough women to make such a sub-analysis statistically meaningful. How sad is that?
The study did have a small subanalysis on how lactation affected risk for diabetes in women with significant risk factors, like women with high BMIs, women who had gestational diabetes during pregnancy, etc. They found:
In the NHS II cohort, higher BMI at age 18 years was associated with shorter duration of breastfeeding, and in both cohorts, duration of lactation was inversely associated with family history of diabetes. Gestational diabetes was not associated with duration of lactation. Nevertheless, adjustment for family history and BMI at age 18 years did not substantially diminish the inverse association between lactation and risk of type 2 diabetes, suggesting that the association we observed was not an artifact of pregravid or pregnancy obesity and its associated insulin resistance. However, stratification by history of gestational diabetes revealed that in this high-risk group of women, lactation did not affect risk of subsequent type 2 diabetes.While it was encouraging that the protective effect of breastfeeding was present for women of size too, it was certainly discouraging that the protective effect did not seem present in women with gestational diabetes. However, a recent smaller tudy (Gunderson 2010) found a lower rate of metabolic syndrome in women with GD who breastfed longer, so further study seems to be indicated.
Regardless, breastfeeding is always worthwhile because of the tremendous immunological benefits and superior nutrition that breastmilk provides to the baby. Furthermore, there is research that suggests that breastfeeding is protective against the baby developing diabetes later in life. For example, Pettitt 1997 found that breastfed infants of Pima Indians (a group at very high risk of diabetes) had less than half the risk for diabetes later in life compared to those who had been bottlefed:
The odds ratio for NIDDM in exclusively breastfed people, compared with those exclusively bottlefed, was 0.41 (95% CI 0.18-0.93) adjusted for age, sex, birthdate, parental diabetes, and birthweight.One important question is how long the maternal benefits of breastfeeding last. The JAMA study did find that as time went on, the protective effects of breastfeeding against maternal diabetes began to fade. They noted:
In these analyses of 2 large prospective cohorts, we found that duration of lactation was inversely associated with risk of type 2 diabetes in young and middle-aged women, independent of other diabetes risk factors, including body mass index, diet, exercise, and smoking status. This association appeared to wane with time since last birth.Perhaps long-term breastfeeding has more of a delaying effect than a prevention effect on diabetes, especially in women with very strong risk factors for the disease.
Another interesting finding was that the longer the period of exclusive breastfeeding, the greater the effect against diabetes. As the authors noted in their discussion:
Our data on exclusive breastfeeding and duration stratified by parity suggest that the length and intensity of breastfeeding with each pregnancy affect the association with diabetes risk. We found that each year of exclusive breastfeeding was associated with a greater risk reduction than total breastfeeding. This may reflect the greater metabolic burden imposed by exclusive breastfeeding.
We also found that longer durations of breastfeeding per pregnancy were associated with a greater benefit, with 1 year’s lactation for 1 child resulting in a 44% reduction in age-adjusted risk, compared with 1 year’s lactation between 2 children resulting in a 24% reduction in risk.
It appears from our analysis of primiparous women that the beneficial association begins to accrue after 6 months of lactation. These data suggest that sustained lactation-associated metabolic changes have more profound effects on diabetes risk.This was an encouraging study because it shows in yet another way just how important breastfeeding is --- not just for the baby, but also for the mother.
However, on a personal note, despite research showing that long-term breastfeeding decreases the risk for type 2 diabetes, I still think there's a very strong possibility that I will get it at some point, despite my 10 years of breastfeeding exposure. PCOS reflects an underlying metabolic abnormality that no one knows how to "fix" at this point, and breastfeeding's improvements in insulin sensitivity and glucose tolerance probably only end up delaying the progression of that metabolic abnormality, not fixing it permanently.
Still, the less time you have diabetes, the less cumulative damage there is from it to your body, so even a delaying effect could have considerable impact on your long-term health. I hold that thought close. And of course I do what I can to lower my risk in other ways.
What About Other Maternal Diseases?
Findings from other studies show that longer breastfeeding duration is not only protective against diabetes, but also against hypertension, high cholesterol, and heart disease. In Schwarz 2009, for example, data from the large Women's Health Initiative study found that longer breastfeeding was associated with lower risk factors and less cardiovascular disease:
Dose-response relationships were seen; in fully adjusted models, women who reported a lifetime history of more than 12 months of lactation were less likely to have hypertension (odds ratio [OR] 0.88, P less than .001), diabetes (OR 0.80, P less than .001), hyperlipidemia (OR 0.81, P less than .001), or cardiovascular disease (OR 0.91, P=.008) than women who never breast-fed, but they were not less likely to be obese. In models adjusted for all above variables and BMI, similar relationships were seen...
Over an average of 7.9 years of postmenopausal participation in the Women's Health Initiative, women with a single live birth who breast-fed for 7-12 months were significantly less likely to develop cardiovascular disease (hazard ratio 0.72, 95% confidence interval 0.53-0.97) than women who never breast-fed...
Among postmenopausal women, increased duration of lactation was associated with a lower prevalence of hypertension, diabetes, hyperlipidemia, and cardiovascular disease.These findings were echoed in another large study (Steube 2009) that found that women who had a lifetime breastfeeding exposure of at least 2 years had lower risk for heart attacks/cardiovascular disease than parous women who had never breastfed.
Compared with parous women who had never breastfed, women who had breastfed for a lifetime total of 2 years or longer had 37% lower risk of coronary heart disease (95% confidence interval, 23-49%; P for trend less than .001), adjusting for age, parity, and stillbirth history. With additional adjustment for early-adult adiposity, parental history, and lifestyle factors, women who had breastfed for a lifetime total of 2 years or longer had a 23% lower risk of coronary heart disease (95% confidence interval, 6-38%; P for trend = .02) than women who had never breastfed.These findings mean that there's a lot of potential room for prevention (or or at least delaying) of diabetes, heart attacks, and other health issues, just by promoting higher rates of breastfeeding....and in particular, promoting breastfeeding for longer durations.