15 sedentary individuals (21 years on average), of which 8 were vitamin C insufficient were recruited. 

At week 4, and the end of the 8 week study, the subjects had to complete a 60 minute treadmill walk. After week 4 all subjects were given 500mg of vitamin C.

The vitamin C insufficient group burned ~25% less fat than the vitamin C sufficient group. 

“fat oxidation during exercise was enhanced by normalizing plasma vitamin C concentrations.”

“vitamin C may be necessary for effective weight management.”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1564400/

A European study involving 13.000 men and women aged 42-82 found that vitamin C is correlated with higher amounts of fat free mass (muscle). 

Group A are the men, group B the women. 

“collagen is a key structural component of skeletal muscle cells and tendons, and carnitine is essential for metabolism of long-chain fatty acids during physical activity”

“more than one-third of men (35%) and one-sixth of women (17%) were vitamin C insufficient.”

“Results suggest that sufficient vitamin C intake may help to reduce age-related loss of skeletal muscle and thus have wide-reaching public health benefit.”

https://academic.oup.com/jn/article/150/10/2789/5897318

A analysis of 29 studies found that taking vitamin C (1-2 grams per day) reduces both the severity, and the duration of the common cold. 

“In adults the duration of colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%).”

https://pubmed.ncbi.nlm.nih.gov/23440782/

An analysis of 9 studies including a total of almost 300.000 subjects found that people who took at least 700mg of vitamin C per day had 25% lower risk of coronary heart disease

https://pubmed.ncbi.nlm.nih.gov/15585762/