Milk and dairy 'good for the brain' claim unproven
"Three glasses of milk every day ‘helps prevent Alzheimer's and Parkinson's’," is the misleading headline in The Daily Telegraph. The study it reports on only found that a high-dairy diet was linked to increased levels of an antioxidant called glutathione.
It is also unclear what, if any, protective effects higher levels of glutathione would have against Alzheimer’s or Parkinson’s disease.
The study, funded by the US Dairy Research Institute, looked at brain MRI scans of 60 adults aged between 60 and 85 using a new technique that could measure levels of glutathione.
This antioxidant is said to "neutralise" potentially harmful chemicals in the brain. Lower levels are found in conditions such as Parkinson’s disease and Alzheimer’s disease, but it is not known whether this is part of the cause of the conditions or a consequence of them.
The level of glutathione was determined once, at the same time as participants were asked about their diets. This study therefore cannot tell us that a high-dairy diet caused the increased levels of glutathione. It is also unable to show what happens to glutathione levels over time or whether the higher levels are protective.
So, all in all, this study proves little. Dairy products are important for bone health and are recommended in moderation as part of a healthy diet, but we just don’t know if they are good for the brain.
Where did the story come from?
The study was carried out by researchers from the University of Kansas Medical Center. It was funded by the US Dairy Research Institute, with further funding provided by the National Institute for Health and the Hoglund Family Foundation. The funding organisations did not have a role in study design, implementation, analysis, or interpretation of data.
The study was published in the peer-reviewed American Journal of Clinical Nutrition.
The Daily Telegraph’s reporting on the story was poor and its headline was inaccurate. It says that people "who guzzled the white stuff were more likely to have healthy brains", when in fact all of the people in the study were healthy. It is also not known whether increased levels of glutathione prevent neurodegenerative disorders, so we can’t say that people with higher levels definitely have "healthier" brains.
The Mail Online’s coverage was slightly more restrained, opting to say that it "may help protect" rather than "will help protect".
What kind of research was this?
This was a cross-sectional study, which measured the level of glutathione in the brain using a new MRI scanning technique. Glutathione is an antioxidant which helps prevent damage to cells. Reduced levels of glutathione have been found in the early stages of Parkinson’s disease, though it is unclear if this might contribute to the development of Parkinson’s or is the result of Parkinson’s.
The researchers wanted to see if drinking milk was associated with higher levels of glutathione in the brain. As it was a cross-sectional study, it only measured the level of glutathione at one time point, and did not follow people up over time to find out what happened to them. This means it was not able to show whether dietary consumption might directly affect glutathione levels in the brain, or indeed whether higher levels were protective against brain diseases such as Parkinson’s disease or Alzheimer’s.
What did the research involve?
The researchers recruited 60 healthy older adults, assessed their dairy intake and measured their level of glutathione in the brain using an MRI scan. They then analysed whether increased consumption of milk was associated with higher levels of glutathione.
The participants were adults aged between 60 and 85, who were healthy and did not have a history of:
- neurologic (brain and nervous system) disorders
- head injury
- claustrophobia (which would make them unsuitable for MRI scanning, as getting a scan involves lying in a small metal tube)
- diabetes
- unstable medical conditions
- lactose or gluten intolerance
- taking glutathione or N-acetylcysteine supplements
The participants completed three 24-hour food frequency questionnaires by telephone with a dietician, and a seven-day diet record was filled in before the MRI scan. From these assessments, the researchers categorised the participants into the following three groups, according to their daily consumption of dairy products:
- low dairy intake, less than one serving per day
- moderate dairy intake, one to two servings per day
- "recommended" dairy intake, three or more servings per day (this was based on US recommendations)
They also had other measurements taken, including body mass index (BMI), waist circumference and body composition of fat and muscle. Finally, they had a brain MRI scan using a new process (known as chemical shift imaging) that had been developed by the researchers to measure the level of glutathione.
The results were then analysed to see if increased dairy consumption was associated with higher levels of glutathione.
What were the basic results?
The participants’ characteristics were similar across the three groups in terms of age, BMI, educational level and quality of their diet.
Glutathione levels in the front and sides (parietal region) of the brain were higher in people who consumed more dairy products, milk and calcium.
The study did not assess whether this difference would affect a person’s health in any way, or how levels fluctuate over time.
How did the researchers interpret the results?
The researchers concluded that "glutathione concentrations were significantly related to adults’ reported consumption of dairy foods and calcium". They say that further research is required to see if increased levels of glutathione prove to be effective in "strengthening cerebral antioxidant defenses [sic] and, thereby, improving brain health in the aging population".
Conclusion
This small study found people with higher dairy, milk and calcium consumption had higher levels of glutathione in the frontal and parietal regions of the brain. Glutathione is an antioxidant that helps to "neutralise" potentially harmful chemicals in the brain.
Research into glutathione and its role in neurodegenerative diseases is in the early stages. It is known that the levels reduce with age and in certain conditions such as Alzheimer’s disease and Parkinson’s disease, but it is not known whether this is part of what leads to the disease or a consequence of the disease. This study does not show whether increasing the level of glutathione would protect against these types of conditions.
This study was cross-sectional, so measured the level of glutathione at one time point in older adults who were healthy. It therefore does not answer the question of whether people with more glutathione in their brains are less likely to develop neurodegenerative disorders.
In addition, previous research has found that in Parkinson’s disease, glutathione levels are only reduced in an area of the brain called the substantia nigra, which is located in the middle of the brain. This study did not look at levels in this part of the brain.
This was a relatively small study, which found a relatively wide range of glutathione levels ranged in different areas of the brain. A much larger study would be required to understand what the normal range is in the population, and how this differs in various disease states. The study is also reliant on self-reporting of dietary intake which can be inaccurate. There is also little information about other factors which could influence the results such as socioeconomic status, ethnicity, family history of Alzheimer’s disease or Parkinson’s disease, other conditions or medication use.
In conclusion, this study has found that increased reported consumption of dairy and milk products was associated with increased levels of the antioxidant glutathione in the brain, but it cannot prove that this was due to the diet or that this will prevent brain disease.
Larger studies into the role of both dairy products and glutathione on neurodegenerative diseases would be useful.
