Could breastfeeding during your childbearing years mean a lower risk of Alzheimer’s in your sixties and beyond?

A provocative new study which has found an association between breastfeeding and a reduced risk of Alzheimer’s disease raises that possibility.

This small study of 81 British women between 70 and 100 years old with and without Alzheimer’s found a “highly significant and consistent correlation” association between having breastfed and a lower incidence of Alzheimer’s.  These associations held when the researchers controlled for age, education history, the age when the woman first gave birth, her age at menopause, and her smoking and drinking history.  However, the association was far less pronounced for women who had a family history of dementia.

The authors found that the longer a woman breastfed, and the longer she breastfed relative to the total time she spent pregnant, the stronger the association with reduced risk of Alzheimer’s.

What could explain this association?  The researchers offered two theories:

The first is that breastfeeding lowers progesterone levels, and that progesterone desensitizes estrogen receptors in the brain.  Estrogen may play a protective role against Alzheimer’s.

But the second theory is one I find interesting because it fits like a puzzle piece into other recent research on breastfeeding and metabolic disorders like insulin resistance.  Here are the other pieces of the puzzle:

Alzheimer’s is characterized by insulin resistance in the brain - the inability to process the glucose that keeps it running.   Insulin resistance in the brain seems to be related to the development of the plaques characteristic of Alzheimer’s.  It’s a strong enough connection that Alzheimer’s has been nicknamed “Type 3 diabetes.”

The authors note that pregnancy induces a natural state of insulin resistance, and that breastfeeding is a means of restoring balance to the system.  So perhaps breastfeeding could be protecting our brains by reducing our risk of insulin resistance later in life.

I find this theory fascinating (and frankly more plausible than the first explanation) because I’ve been keeping my eye on a raft of recent research showing that women who breastfeed are less likely to develop insulin resistance and otherwise be metabolically disturbed.  We know that breastfeeding reduces mothers’ risk of Type II diabetes later in life.  And we also know that women who have gestational diabetes in pregnancy and then breastfeed are more protected against metabolic syndrome (including insulin resistance) than women who don’t.

So, bottom line:  Is it possible that the insulin resistance associated with not breastfeeding is related to the development of Alzheimer’s?  The authors connect the dots like this:

“Women who spent more time pregnant without a compensatory phase of breastfeeding therefore may have more impaired glucose tolerance, which is consistent with our observation that those women have an increased risk of Alzheimer’s disease.”

There are many factors related to the development of Alzheimer’s, including genetic mutations.  The fact that this study found a far less pronounced effect of breastfeeding in women with a family history of dementia is evidence of the complexity of this disease.

Obviously, this is a small study, and these findings have to be taken with a grain of salt until (and if) they’re replicated they’re with a much larger group of women.  But this study, and its suggestion of a biological model for how breastfeeding could affect brain health, offers some fascinating questions for future investigation.