More vitamin C, more muscle
The more vitamin C there is in your diet, the more muscle mass you have. British epidemiologists at Norwich Medical School stumbled upon the association in a study involving 13,000 men and women.Study
The researchers used data from 13,000 English men and women aged 42-82 who participated in the European Prospective Investigation into Cancer and Nutrition. The researchers knew the fat free mass - which consists mainly of muscle mass - of the study participants.

Vitamin C intake

The researchers determined the participants' intake of vitamin C, and then divided the study participants into 5 groups of approximately equal size according to their intake. Those groups are called quintiles. Only the 2 quintiles with the highest intake consumed 80-90 milligrams of vitamin C per day or more.According to the EFSA, men and women need 90 or 80 milligrams of vitamin C per day, respectively. Sixty percent of the study participants did not meet that guideline. It is remarkable that the difference between the quintile with the lowest intake and the quintile with the highest intake is equal to the amount of vitamin C in an orange.
As the study participants consumed more vitamin C, their fat free mass was larger.
Click on the figures for a larger version.

Vitamin C status
The researchers measured the concentration of vitamin C in the blood of the study participants, and divided their population into two groups - one with sufficient vitamin C [more than 50 micromoles vitamin C per liter] and a group with too little vitamin C. [less than 50 micromoles of vitamin C per liter].

Click on the figure below for a larger version.

The researchers again found a relationship between fat free mass and vitamin C. Fat free mass was greater in the group with a healthy vitamin C status.Conclusion
"This study has shown significant positive associations between both dietary and circulating vitamin C and measures of skeletal muscle in a large cohort of free-living middle- and older-aged men and women", write the researchers.

"These results suggest that ensuring sufficient dietary vitamin C intake, by promoting a diet rich in fruits and vegetables, may help to reduce age-related loss of skeletal muscle and thus have wide-reaching public health benefit."
J Nutr. 2020 Aug 27;nxaa221. doi: 10.1093/jn/nxaa221. Online ahead of print.