Breastfeeding Duration and Risk of Mortality Among US Women
by Anne Eglash MD, IBCLC, FABM
What is the relationship between lifetime duration of breastfeeding and risk of maternal death?
There is mounting evidence regarding the differences in health between women who breastfeed and those who don’t. Women who don’t breastfeed, or who breastfeed for short periods of time, have a higher risk of many illnesses including cancer (particularly breast and ovarian), high blood pressure, high cholesterol, heart disease, stroke, diabetes, and endometriosis.
The authors of the study for this week looked at the relationship between breastfeeding duration and maternal mortality.
The authors used 2 sets of data, the Nurses Health Study (NHS), and the Nurses Health Study II (NHSII) because they provide an abundance of demographic, lifestyle, and health data over 3 decades. In addition, the studies have collected data on the duration of breastfeeding, described as ‘cannot remember’, ‘did not breastfeed’, <1, 1-3, 4-6, 7-11, 12-17, 18-23, 24-35, 36-47, and ≥ 48 months.
The NHS and NHS II studies recruited 121,700 nurses in 1976 and 116,329 in 1989, respectively. Because they excluded women who didn’t carry a child to at least 24 weeks, or who already had cardiovascular disease or cancer at the time of enrollment, there were a total of 166,708 women in the final analysis.
They found that the women with the greatest number of months of lactation had lower mortality rates.
What else? See the question!
- The only reason that breastfeeding women had lower mortality is because of a lower rate of death from breast cancer.
- Breastfeeding is associated with lower mortality risk because women who breastfed have healthier lifestyles than women who didn’t.
- Breastfeeding reduces the risk of mortality by 5-7%.
- Breastfeeding for a total of 15 months is not more protective from death than breastfeeding for 9 months.
See the Answer
Abstract
Background
Breastfeeding has been associated with a reduced maternal long-term risk of chronic diseases, but its association with mortality is poorly known.
Methods
We included 166,708 female United States (US) nurses from the Nurses’ Health Study (1986-2016) and the Nurses’ Health Study II (1989-2019) who experienced at least one pregnancy lasting at least six months across their reproductive lifespan. Hazard ratios and 95% confidence intervals (CI) for mortality according to lifetime breastfeeding duration were estimated with time-dependent Cox proportional hazards regression models.
Findings
During 4,705,160 person-years of follow-up, 36,634 deaths were documented in both cohorts, including 9880 from cancer and 7709 from cardiovascular disease (CVD). Lifetime total breastfeeding duration was associated with a lower subsequent risk of all-cause mortality in a non-linear manner (p-value for non-linearity=0.0007). The pooled multivariable-adjusted hazard ratios of all-cause mortality were 0.95 (95% CI: 0.92 to 0.98), 0.94 (95% CI: 0.91 to 0.98), 0.93 (95% CI: 0.90 to 0.97), and 0.93 (95% CI: 0.89 to 0.97), respectively, for women reporting lifetime total breastfeeding duration of 4−6, 7−11, 12−23, and ≥24 months, compared to women who breastfed for ≤3 months over their reproductive lifespan. Cause-specific analysis showed a similar pattern of non-linear inverse associations between life-time total breastfeeding duration and CVD and cancer mortality (both p-values for non-linearity <0.01). There was no evidence of interactions between breastfeeding duration and pre-pregnancy lifestyle factors on mortality risk.
Interpretation
Parous women with longer lifetime breastfeeding duration had a modest lower risk of mortality.
After adjusting for multiple confounders including age at first birth, infertility, smoking status, alcohol intake, exercise intensity, healthy eating index and BMI, the researchers still found that longer lifetime total breastfeeding duration was associated with a 5-7% lower risk of mortality later in life. In other words, shorter duration of breastfeeding increases the risk of mortality in one’s age group.
Breastfeeding duration was associated with a decreased risk of all-cause mortality. Longer breastfeeding rates were associated with a lower risk of cardiovascular disease and cancer, as well as fewer deaths from respiratory cancers, endocrine, nutritional, metabolic and immunity disorders.
The protective effect of breastfeeding on mortality is dose related, with more cumulative months of breastfeeding being more protective than fewer months.
There are many theories as to why breastfeeding reduces maternal mortality. Pregnancy increases cholesterol, fat accumulation, and insulin resistance, all of which can increase the future risk of cardiovascular disease and cancer. Breastfeeding helps to mobilize visceral fat stores, regulate insulin secretion, improve cholesterol, and improve pancreatic function. All of these changes reverse the metabolic changes associated with pregnancy, thereby reducing the risk of mortality from cardiovascular disease and cancers.
Aruna Sangisetty
Death and breastfeeding is more coincidental and lifestyle choices and eating habits possibly is the cause of the difference
Before the formula days when breastfeeding was norm for women death rates were no different
IABLE
Actually, this study does not support your comment. This research shows that the association between breastfeeding and mortality is NOT about a difference in lifestyle, since they were able to measure healthy eating and exercise indices. When healthy eating and exercise were taken into account, there was still a difference in mortality. Breastfeeding women had less cardiovascular and cancer mortality than non-breastfeeding women. This makes sense, since we understand the protection that breastfeeding affords against cardiovascular disease, breast and ovarian cancer.
Aruna Sangisetty
Just like Breastfeeding is norm healthy eating especially fresh unprocessed and non additive diet is also norm
Lot of physical activity is also norm
In general women now with breast feeding living some what closer to that natural life style may be the cause
This is just my hypothesis!!
IABLE
I would say that physical activity and healthy eating are not necessarily the norm among people who have breastfed. As a family physician, I have watched my lactating patients grow old over 30 years, and I know for a fact that this is presumptuous. It is also presumptuous to assume that people who didn’t lactate don’t have healthy diets and exercise. In fact, many people who didn’t lactate or who lactated for a short period had a high intention to breastfeed (the same characteristics as those who successfully breastfed) but were unable to due to insufficient glandular tissue or other factors out of their control.
Tara Williams
Interesting study. Thanks for sharing Anne. Yet more data to support breastfeeding as beneficial not just for the baby but also for the mom.