A study of 2,044 elderly Japanese people found that those with lower levels of vitamin C in their blood plasma tended to have lower gray matter volume in their brains, as well as lower connectivity between a collection of brain regions known as the default mode network. Haruka Nagaya of Hirosaki University in Japan and colleagues present these findings in the open access journal PLoS One on June 10, 2026.
Previous research has found associations between diets higher in vitamin C and a lower risk of cognitive decline in older adults. However, few studies have directly examined plasma vitamin C levels and possible associations with brain structure and connectivity within brain networks. To fill this gap, Nagaya and colleagues analyzed magnetic resonance imaging (MRI) scans and plasma vitamin C levels of 2,044 Japanese adults over 64 years of age.
Specifically, they measured the volume of each participant’s gray and white brain matter (calculating individual differences in total brain volume between participants). They also assessed connectivity within the default mode network, which is associated with many cognitive functions, such as attention and autobiographical memory.
After 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 blood plasma levels of vitamin C could potentially support cognitive function and counteract cognitive decline. However, the findings do not confirm any such cause-and-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 obtaining repeated measurements of plasma vitamin C over time, taking into account additional lifestyle and dietary factors, and including participants with additional ethnicities and socioeconomic status.
Tomohiro Shidaku adds:Our study shows 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 cognition. This finding raises the intriguing hypothesis that a diet rich in vitamin C may play a supportive role in maintaining brain health and mitigating age-related cognitive decline in older adults.”
“What I found most exciting about this research is that we were able to detect these subtle but significant associations between a single dietary factor and large-scale brain networks using a robust, community-based cohort of over 2,000 older adults. It really highlights the potential impact of our daily eating habits on our brain structures.”
