Study links low vitamin C levels in the blood plasma to reduced brain connectivity

A study of 2,044 older Japanese adults found that those with lower vitamin C levels in their blood plasma tended to have a lower volume of gray matter in their brains, as well as lower connectivity amongst a collection of brain regions known as the default mode network. Haruka Nagaya of Hirosaki University, Japan, and colleagues present these findings in the open access journal PLOS One on June 10, 2026.

Previous research has uncovered associations between diets higher in vitamin C and lower risk of cognitive impairment in older adults. However, few studies have looked directly at vitamin C levels in blood plasma and potential associations with brain structure and connectivity within brain networks. To help fill that gap, Nagaya and colleagues analyzed magnetic resonance imaging (MRI) scans and plasma vitamin C levels of 2,044 Japanese adults over the age of 64.

Specifically, they measured the volume of each participant's gray and white brain matter (accounting for individual differences in total brain volume between participants). They also evaluated connectivity within the default mode network, which is associated with several cognitive functions, such as attention and autobiographical memory.

After statistically accounting for other factors that could affect brain structure and connectivity-such as age, physical activity habits, and education level-the researchers found that participants with lower plasma vitamin C levels tended to have lower gray matter volume, as well as lower connectivity within the default mode network.

These findings suggest the possibility that optimal levels of vitamin C in blood plasma could potentially support cognitive function and counteract cognitive decline. However, the findings do not confirm any such cause-effect relationship between vitamin C levels and brain health, and further research is needed to explore the biological mechanisms behind the observed statistical associations.

The authors also note that future research could build on this study by taking repeated plasma vitamin C measurements over time, accounting for additional lifestyle and nutritional factors, and including participants of additional ethnicities and socioeconomic status.

Tomohiro Shintaku adds: "Our study demonstrates that higher plasma vitamin C levels are associated with better preserved structural connectivity of the default mode network (DMN), a key brain network involved in cognitive function. This finding generates the exciting hypothesis that a diet rich in vitamin C might play a supportive role in maintaining brain health and mitigating age-related cognitive decline in older adults."

"What I found most fascinating about this research is that we were able to detect these subtle but significant associations between a single nutritional factor and large-scale brain networks by utilizing a robust, community-based cohort of over 2,000 older adults. It truly highlights the potential impact of our everyday dietary habits on our brain structures."