Does breastfeeding lower Alzheimer's risk?

"Mothers who breastfeed may have a decreased risk of Alzheimer's disease in later life," The Independent advises. The news comes from research that suggests that the biological processes that occur during breastfeeding may have a protective effect against the disease.

The study examined the relationship between reported breastfeeding history and the risk of Alzheimer's disease among 81 elderly white British women both with and without Alzheimer's disease. Researchers carried out interviews with the women to determine whether or not they breastfed and if so, for how long. They also gathered information from their family and carers.

The researchers found that any history of breastfeeding was associated with a lower risk of Alzheimer's disease compared with women who had no history of breastfeeding. They also found that a longer time spent breastfeeding was associated with a lower risk of Alzheimer's.

Despite these findings, this research does not provide evidence of a direct cause and effect between breastfeeding and a reduced risk of Alzheimer's disease, merely an association.

The study only had a small sample size and relied on self-reporting from participants. This presents difficulties with reliable information, especially as some of the women involved were affected by dementia.

Despite the limitations of this study, breastfeeding offers a host of benefits to both mother and baby, such as lowering the risk of breast cancer.

Where did the story come from?

The study was carried out by researchers from the Universities of Cambridge and Manchester in the UK and the University of Utah in the US. It was supported by the Gates Cambridge Trust and Gonville and Caius college. It was published in the peer-reviewed Journal of Alzheimer's Disease.

The study participants reportedly received a "modest gift voucher" for their participation in the study.

The story was covered widely and was mainly reported on accurately, apart from some misleading headlines that suggested there is a causal link between breastfeeding and Alzheimer's.

The Independent incorrectly reported that the study was a "pilot study", but it is unclear where this information came from as this was not mentioned in the study publication.

What kind of research was this?

This was a case-control study investigating the role of breastfeeding history on the risk of Alzheimer's disease among a group of 81 elderly white British women.

A case-control study is a comparison of people who have a condition of interest (cases – women who breastfed) with those who don't (controls – women who didn't breastfeed). The past histories and characteristics of the two groups are examined to see how they differ.

What did the research involve?

The researchers initially interviewed a total of 131 white British women over the age of 70 and living in England, including women both with and without Alzheimer's disease.

After the initial interview, researchers then carried out a more detailed analysis of the results for 81 women who had at least one child as well as complete data available, such as their breastfeeding history or family history.

Participants were recruited through nursing homes, churches, retirement community centres, the UK Alzheimer's Society and a retired employee community.

Participants were excluded if they had been diagnosed with non-Alzheimer's-type dementia (such as vascular dementia or Parkinson's disease) and any possible external brain injury or brain tumour.

Participants underwent interviews where information was collected on their reproductive and breastfeeding history. To determine breastfeeding history, the women were asked whether or not they breastfed and how long they had breastfed for. The researchers also spoke to the participants' relatives, spouses and carers to confirm what had been reported.

Dementia status was assessed by a certified researcher using the clinical dementia rating (CDR) scale. The CDR, which the authors report is an effective diagnostic tool, consisted of a 60-90 minute interview with the participant, as well as with their relative or carer. CDR scores were rated as:

• 0 – no dementia
• 0.5 – questionable dementia
• 1 – mild dementia
• 2 – moderate dementia
• 3 – severe dementia

The results of these CDR scores were used to estimate the age at onset of dementia for each participant who had a CDR score of more than zero.

Alzheimer's disease risk was defined as the time between when the participant was aged 50 and a transition from a CDR scale of 0 (no dementia) to 0.5 (questionable dementia), up until the age the participant was interviewed.

Using the findings from the interviews, the researchers then calculated the following:

• total amount of months spent breastfeeding
• average amount of breastfeeding per full-term pregnancy
• ratio between the total amount of months spent breastfeeding and total amount of months spent pregnant
• whether a woman at risk of Alzheimer's disease had breastfed

The researchers then analysed the results for women with and without a family history of dementia, with family history defined as having a parent or sibling who likely had dementia, as reported by the participant and their family members.

In their analysis, the researchers first adjusted the results for the age of the participants at interview, education, occupation, oestrogen (hormone) replacement therapy use, removal of ovaries (oopharectoomy), age at first birth and age at menopause.

What were the basic results?

Of the 81 women included in the analysis, there were 40 women who were "cases" who had questionable dementia or mild, moderate or severe dementia (CDR score of more than zero), and 41 women were "controls" who did not have dementia (CDR score of zero).

The main results of the study were:

• longer breastfeeding duration was significantly associated with a lower risk of Alzheimer's disease (p<0.01)
• women who breastfed had a lower risk of Alzheimer's disease than women who did not breastfeed (p=0.017)

After adjusting for the effects of occupational history and education, results were still found to be significant. For the cases, the researchers estimated the age at transition from a CDR score of 0 (no dementia) to 0.5 (questionable dementia) among women with CDR scores above zero was approximately 74.8 years.

For women without a family history of dementia (n=61), breastfeeding was found to decrease the risk of Alzheimer's disease.

For women with a family history of dementia (20), the influence of breastfeeding on risk of Alzheimer's disease was significantly lower than for women with a family history of dementia.

How did the researchers interpret the results?

The researchers concluded that longer breastfeeding duration was associated with a lower risk of Alzheimer's disease. Any history of breastfeeding compared with no history of breastfeeding was also associated with a reduced risk of the disease.

The authors report that these overall findings could be because of the beneficial effects of breastfeeding on progesterone deprivation (hormone deprivation), restoring insulin sensitivity, or both.

Progesterone deprivation reduces the levels of hormones known to be associated with an increased risk of breast and ovarian cancer. Restoring insulin sensitivity helps improve the efficiency of the body's metabolism and reduces the risk of diabetes developing.

However, both of these ideas are just unproven hypotheses and further research would need to be conducted to confirm them.

Conclusion

Overall, this study provides some limited evidence of an association between breastfeeding, length of time spent breastfeeding and the risk of Alzheimer's disease. It does not provide evidence of a direct cause and effect relationship, only that there seems to be an association. 

However, there are some other limitations to this study:

• Whether or not women breastfed and how long they breastfed for was determined by self-reporting, which can make the results less reliable, particularly as the participants (some of which were considered to have dementia) were asked to recall breastfeeding events from some time ago. The authors did attempt to account for this by asking the participants' spouse or carer to confirm what was reported, but this does not entirely account for errors in reporting.
• The study only included white British women living in England, so the study findings may not be applicable to people from other ethnic backgrounds or those who live in other countries.
• The age at which women might have transitioned to dementia (from a CDR score of zero, indicating no dementia, to a CDR score of more than zero, indicating questionable dementia) was based on the degree of dementia determined at interview. Although this method provided estimates, it may not have accurately captured when and if women did actually transition from no dementia to dementia.

Consequently, headlines such as "Breastfeeding 'lowers Alzheimer's risk' " reported by The Daily Telegraph do not accurately reflect the findings of this study.

In spite of these limitations, breastfeeding where possible has many benefits for both mother and baby.