“Drink your milk.” That’s an instruction parents have been giving their kids for eons. Dairy milk, a rich source of calcium and vitamin D, has long been recognized for its role in helping children develop healthy bones and teeth.

But maybe it is the kids who should be instructing the adults. Recent research conducted at the University of Kansas Medical Center has found that milk consumption can also benefit the brains of older adults by guarding against cognitive decline.

The KU Medical Center research team found that adults aged 60-89 who drink three cups of dairy milk a day can boost their brains’ levels of glutathione (GSH), a powerful antioxidant that helps protect the brain from some of the damage that accompanies aging and aging-related diseases.

“Just this simple drinking of milk was able to raise that antioxidant level up in these older adults, which is impressive from a single food you can buy at the grocery store,” said Debra Sullivan, Ph.D., RD, professor and chair of the Department of Dietetics and Nutrition in KU School of Health Professions. Sullivan is an author on the study, which was published in August 2022 in Frontiers in Nutrition.

A Unique Scanning Technique

Like an old car that rusts, the human brain becomes corroded over time by free radicals and other oxidants that are released as the brain converts nutrients into energy. This oxidative stress, as it’s called, is believed to be a major mechanism of brain aging as well as many neurodegenerative diseases including Alzheimer’s and Parkinson’s. GSH helps stave off oxidative stress and the damage it causes. But as people age, their levels of brain GSH tend to drop.

The U.S. Dietary Guidelines recommend that adults drink three cups of milk a day, but according to data from the Centers for Disease Control and Prevention, the typical American adult over age 60 drinks less than two.

Sullivan became interested in studying GSH, the brain’s major antioxidant, and brain health more than a decade ago when she began collaborating with In-Young Choi, Ph.D., lead author on the study and director of the Metabolic Imaging Unit and the Magnetic Resonance Science Program at the Hoglund Biomedical Imaging Center at KU Medical Center.

Choi, also a professor in the Department of Neurology who focuses on brain aging and neurodegeneration, had worked with Phil Lee, Ph.D., a professor of the Department of Radiology, to develop a novel magnetic resonance imaging technique that can measure the level of antioxidants in the brain. These unique scans use special imaging techniques based on a multiple quantum physics concept and can selectively detect GSH in different parts of the brain simultaneously.

“There are not many facilities in the world that can measure these brain antioxidants in humans,” said Sullivan. “When I found out we had this capability at KU Medical Center, I wanted to look at what foods people were consuming and compare it with what their brain antioxidant status was.”

Sullivan approached Choi about using Choi’s brain antioxidant scanning technique to measure how what people eat affects their brain. When they completed their first exploratory study, they were surprised by the results.

“I was thinking fruits and vegetables would be highly correlated with antioxidants in the brain,” remembered Choi. “But instead, it was dairy, and among the dairy foods, it was milk. That was really surprising.”

The Milky Way

The researchers applied for and were awarded a grant from the National Dairy Council, which, along with a National Institutes of Health (NIH) grant that funds the Hoglund Biomedical Imaging Center, supports their work. These funders have no input on the study design, data, the interpretation of the data or the writing the manuscript, Sullivan noted.

In 2015, Sullivan and Choi and their team published an observational study in the American Journal of Clinical Nutrition that again found that milk was highly correlated with concentrations of GSH in the brains of older adults. The next step, the most recent study, was designed to see what would happen to a person’s brain GSH if that person increased their milk consumption.

In this research, 73 adults aged between the ages of 60 and 89 who typically consumed less than 1.5 servings of dairy per day were randomly assigned into a control group, which did not alter its usual milk intake, and into an intervention group, which increased their milk intake to three cups per day for three months. The study provided the participants in the intervention group with low-fat 1% milk delivered weekly from Kansas City area grocery stores.  For participants in both groups, brain antioxidant imaging scans were conducted at baseline and after three months.

While there was no change in the levels of GSH in the brains of the participants in the control group, the group that drank three cups of dairy milk a day saw their brain GSH levels increase by an average of nearly 5% overall and by more than 7% in the parietal region of the brain.

Choi noted that earlier findings have shown that GSH levels are lower in older adults by about 10%. “So, by drinking milk, it looks like you can catch up some,” she said.

Moreover, the daily three cups of milk that increased the levels of brain GSH is already the amount recommended for adults by the U.S. Dietary Guidelines. The “side effects” when an older person begins drinking this much milk to protect the brain include helping to increase their muscle mass and preventing them from developing osteoporosis and breaking bones.

“Milk has a great package of nutrients. It’s important for your brain health, your bone health, your muscle health, all of those things,” Sullivan said. “That’s the takeaway.”

An Optimal Package of Nutrients

The researchers have focused on cow’s milk, rather than other dairy foods, because in their observational study, milk appeared to increase GSH production more than other foods including cheese and yogurt. They theorize that it is milk’s specific mix of nutrients, not present to the same degree in other dairy products, that makes this difference.

A GSH supplement from a vitamin store will not have the same effect, said Choi, because it taken as a supplement, GSH will not enter the brain. Instead, the brain must synthesize three amino acids —glycine, glutamate, and cysteine— to make GSH. “So that's why you cannot just take ta pill and then get increase,” said Choi. “You basically have to provide those foods or ingredients that will make those antioxidants.”

Dairy milk is an excellent source of all three amino acids. Compared with other foods, the whey protein in milk has particularly high levels of cysteine, which is particularly important for the body to make more GSH. Compared with yogurt and cheese, milk is also especially rich in the vitamin riboflavin and calcium, which are required for GSH maintenance.

What future studies can determine is the specific mechanism by which the nutrients in milk increase the levels of GSH in the human brain. The researchers also plan to conduct a larger study as well as studies including cognitive tests to measure if milk is leading to measurable changes in brain function and if there is an optimal dose of milk and if the amount of milk fat matters. Future research is also needed to see if other types of milk, such as goat and sheep milk and plant-based milks, could have a similar benefit.

In the meantime, Sullivan sees no reason for older adults to wait to make sure that they are getting three cups of dairy milk each day. For people who are lactose-intolerant, lactose-free milk should work as well as regular milk for boosting GSH, she said. Sullivan pointed out that there are ways to incorporate more milk into a person’s diet other than drinking it out of a glass.

“An easy way would be to pour it over cold or hot cereals. You could add your favorite fruits, vegetables, yogurt and ice to the milk and make a smoothie,” she said. “You can always incorporate milk into foods such as soups, puddings, macaroni and cheese, and many others. If you are creative, you can think of numerous ways to incorporate milk into what you eat each day.”