These latest study findings add to the mounting evidence linking vitamin C to cardiovascular health, which the researchers argued has had mixed results so far.
“[Previous] studies showed some limitations, including suboptimal adjustment for potential confounders such as fiber intake,” wrote the two authors, Nerea Martín-Calvo and Miguel Ángel Martínez-González, in their study published in Nutrients.
Both are associated with the University of Navarra in Spain as well as the Carlos III Institute of Health in Madrid. Martínez-González is also associated with the Harvard T.H. Chan School of Public Health. The large cohort of study participants are all part of the ongoing Seguimiento Universidad de Navarra (SUN) study, which is made up of Spanish university graduate students and alumni.
Enrolment to the pool of study participants was permanently open, and follow-up information is gathered by mailed questionnaires every two years.
Of the 22,280 participants recruited before March 2014, the final number used in this vitamin C study came after excluding participants due to various reasons, including 308 participants due to prevalent cardiovascular disease, 7,384 participants younger than 40 years old (considered too young to present a cardiovascular event during the follow-up).
The questionnaire asked participants to identify how often in the past year they consumed food and beverage items from a list of 136 items. This information helped researchers takeinto account not just vitamin C intake, but other variables such as fiber and energy (calorie) consumption.
Crunching the numbers
Researchers divided participants’ vitamin C intake into tertiles, from high to low. They found that participants in the highest tertile were older, more likely to be female, less likely to be current smokers, physically active, and spent less time watching television.
Additionally, the upper tertile participants reported higher fiber intake, adhered to a Mediterranean diet pattern, and were more likely to take vitamin C supplements. “We found total vitamin C intake showed a modest correlation with energy intake, but it was highly correlated with total fiber intake,” they wrote.
They also found that cardiovascular conditions such as aortic aneurism, heart failure, and hypertriglyceridemia at baseline were less prevalent among the higher vitamin C intake group. However, they did find the higher vitamin C group to be more prone to hypertension, venuous thrombosis, diabetes, and cancer, “probably due to the older age of participants [in this tertile].”
It’s in the fruits and vegetables
The self-reporting nature of the study was one major limitation in the study, the participants admitted. Another was the relatively narrow sample of participants. “The SUN cohort is not a representative sample of the general population,” they wrote. “Therefore generalization of these results must be based on biological mechanisms rather than on statistical representativeness.”
Another issue was separating vitamin C from fiber intake, especially with the consumption of fruits and vegetables, as vitamin C and fiber were highly correlated. Though previous studies have observed vitamin C’s effect on cardiovascular health, researchers in this current study argued that these findings are the first to account for fiber intake by using a residuals method (adjusting numbers to nullify correlation with fiber).
The researchers called for reproduction of this analysis on different populations before clinical implications can be assessed. A similar study analysing a link between vitamin C and cardiovascular health using a large sample was conducted in Denmark, and published in The American Journal of Clinical Nutrition in 2015.
“Further research is needed in order to fully understand the biological mechanisms explaining these associations,” the researchers wrote. Moreover, these results must be reproduced in different populations before clinical implications can be assessed.
Published online ahead of print, doi:10.3390/nu9090954
Vitamin C Intake is Inversely Associated with Cardiovascular Mortality in a Cohort of Spanish Graduates: The SUN Project
Authors: Nerea Martín-Calvo and Miguel Ángel Martínez-González