Longer duration of lactation and breastfeeding was associated with a reduced risk of age-related macular degeneration later in the mother’s life, according to the Tromsø Study conducted in Norway.
The study is believed to be the first to address the effect of lactation on maternal AMD, the study authors said. They explored that association to explain the disparity in AMD risk between men and women.
Investigators were unable to attribute the correlation between breastfeeding and reduced risk of AMD to specific biological or clinical factors, first author Maja G. Erke, MD, PhD, said in an interview with Ocular Surgery News.
“There are some papers about how breastfeeding can protect women from high blood pressure later in life,” Erke said. “So, maybe it has something to do with a better cardiovascular profile, or maybe the lactation hormones interact with other molecules or components in the retina.”
Breastfeeding is popular and use of hormone replacement therapy is uncommon in Norway, Erke said.
“More than 60% of the women have breastfed all of their kids more than 3 months,” she said. “But hormone replacement was not very common at all. So, that could do something with the power of the study.”
The study was published in the British Journal of Ophthalmology.
Patients and methods
The sixth Tromsø Study, a prospective population-based cohort analysis, included 1,512 postmenopausal women aged 60 years to 87 years. The sixth survey was the first to include extensive eye examinations.
All participants underwent a complete physical examination, blood testing and retinal photography, and completed questionnaires on reproductive history, smoking, alcohol use, diet, exercise, duration of breastfeeding, and use of contraceptives and/or hormone replacement therapy.
Non-fasting blood samples were analyzed for blood glucose and serum cholesterol levels.
Patients self-reported intake of fatty fish, cod liver oil, omega-3, vitamin and mineral supplements, and fruits and vegetables.
“The statistics analyses of the relationship between breastfeeding and AMD were tested in different ways,” Erke said. “That was, breastfeeding per child and breastfeeding all children more than 3 months, more than 4 months and more than 6 months. All were significantly related to lower prevalence of late AMD controlled for confounders.”
Forty-eight women (3.2%) had late AMD, and 378 (25%) had at least one drusen larger than 125 µm.
Data on childbirth were available for 1,470 subjects, and data on breastfeeding were available for 1,168 subjects.
Results and analysis
Accounting for age, medical history and reproductive history, women who had breastfed all their children for at least 6 months had an odds ratio of 0.09 for presence of end-stage AMD.
Duration of breastfeeding per child as a continuous variable correlated strongly with reduced odds for late AMD; the odds ratio per month of breastfeeding each child was 0.80.
There were no relationships between AMD and contraceptive use, hormone replacement therapy, age at first childbirth and age at menopause. Relationships between breastfeeding and smoking history, systolic blood pressure and BMI were insignificant.
Inexplicably, intake of fatty fish and omega-3 fish oil supplements had an insignificant impact on the risk of AMD, Erke said.
“That was also a noteworthy finding, I think,” she said.
Investigators plan to conduct another installment of the Tromsø Study in 1 or 2 years, Erke said.
“We are working on a paper about cardiovascular risk factors,” she said. “There are some [optical coherence tomography] studies ongoing. We have the OCTs from all of these participants. It’s a work in progress.” – by Matt Hasson
Erke MG, et al. Br J Ophthalmol
For more information:
Maja G. Erke, MD, PhD, can be reached at University Hospital North Norway, Department of Ophthalmology, N-9038 Tromsø, Norway; 47-915-07766; fax: 47-776-26366; email: email@example.com
Disclosure: Erke received a PhD grant from the Northern Norway Regional Health Authority.