Low levels of immune-boosting vitamin now linked to decline in brain function, study suggests

Vitamin C may do more than bolster the immune system – new research suggests it could help protect the aging brain.

A study of older Japanese adults found that lower blood levels of the vitamin were linked to reduced gray matter volume and weaker connectivity in brain networks affected early in Alzheimer’s disease.

Gray matter is the brain tissue that contains nerve cells responsible for memory, thought, and decision-making. When it shrinks, the brain loses processing power, which can affect memory and reasoning.

The association held even after adjusting for age, lifestyle and other risk factors, and experts say the effect was comparable in magnitude to established vascular and lifestyle dementia risks.

While the findings do not prove causation – people with higher vitamin C levels tend to have healthier overall diets – they add to a growing body of evidence linking the nutrient to cognitive health.

Researchers said that while no single nutrient can stave off dementia on its own, a consistently nutrient-rich diet, including vitamin C from fruits and vegetables, may support long-term cognitive health. 

More than seven million Americans are currently living with Alzheimer’s disease, which causes progressive memory loss, confusion and difficulty with everyday tasks.

The disease typically affects gray matter and the default mode network – the same brain regions where the new study found reduced volume and weaker connectivity in participants with lower vitamin C levels.

Researchers analyzed data from more than 2,000 older Japanese adults with an average age of 70, who were part of a larger health study.

All participants underwent brain scans using a high-powered MRI machine that measured total brain size, gray matter volume and volume of white matter, which is made up of the wires that connect different parts of the brain, enabling them to communicate with one another.

To assess brain connectivity, researchers used a technique called source-based morphometry, which looks for patterns of coordinated structure across different brain regions.

This allowed them to identify and measure the strength of the default mode network, a set of brain areas that work together during memory, self-reflection and daydreaming.

Blood samples were taken after an overnight fast to measure vitamin C levels.

Researchers then analyzed whether those levels were linked to brain volume and network connectivity, while accounting for age, sex, education, cognitive test scores, medical conditions, and lifestyle habits like smoking, drinking, and exercise.

Researchers also adjusted all brain volume measurements for individual head size to ensure fair comparisons.

The study, published in the journal PLoS One, reported that people with higher vitamin C levels tended to have more gray matter.

Specifically, higher vitamin C levels were associated with a small but measurable increase in gray matter volume, and the finding was statistically significant, meaning it’s unlikely to be due to chance.

That effect was comparable in size to the impact of other known risk factors like high blood pressure or smoking.

Vitamin C levels were also linked to how well different brain regions communicate. People with higher vitamin C had stronger connections in two key parts of the brain’s default mode network involved in memory and self-reflection.

The relationship was significant for both the front part of the network and one of the rear sections. A third network component that tends to become more active with age showed a weaker connection in people with higher vitamin C.

The researchers see this as a potential sign that vitamin C may help slow age-related changes in brain wiring.

Looking closer at specific brain areas, higher vitamin C was tied to more preserved tissue in the posterior cingulate cortex, a region that is among the first to be affected in Alzheimer’s disease.

Other affected areas included the middle cingulate cortex, the medial prefrontal cortex, and regions near the temples, all of which are involved in emotional regulation, complex reasoning, and language processing, respectively.

The effects were modest. The correlation coefficients ranged from about 0.06 to 0.12 on a scale where zero means no relationship and one means a perfect relationship.

But the researchers note these are similar to those seen for established risk factors like blood pressure and blood glucose in large-scale studies and could still be meaningful at the population level over a lifetime.

The researchers stress that the study does not prove vitamin C prevents dementia. But they say the findings add to growing evidence that good vitamin C status may support brain health in older adults.

The recommended daily intake of vitamin C is 90 milligrams for adult men and 75 milligrams for adult women. Smokers need a bit more — about an extra 35 milligrams per day — because smoking depletes the body’s vitamin C stores.

Because the human body cannot produce or store vitamin C, it must be obtained daily through food. Fortunately, it’s found in a wide variety of fruits and vegetables.

Excellent sources include citrus fruits like oranges and grapefruit, as well as kiwi, strawberries, cantaloupe and papaya. On the vegetable side, red and green bell peppers, broccoli, Brussels sprouts, tomatoes, potatoes and leafy greens like spinach and kale are all packed with vitamin C.

Juice is also a great option. About three-quarters of a cup of orange juice provides enough vitamin C to meet the daily requirement for most people.