Looking younger with exercise-Correlation does not always mean causation

I can't recall the details of the source- i.e. whether I heard and/or read about the rejuvenation effect of exercise- but as I recall the report mentioned that following an exercise program the skin texture of the participants made them look younger.
Before accepting this as scientific proof my usual word of caution when dealing with clinical scientific experiments :  "Correlation does not necessarily mean Causation " -its just one of the 4 levels of scientific proof- and only the 3rd highest category . In increasing order of proof they are:
       1. Testimonial
       2. Argumentative
       3. Correlative
       4. Gold scientific standard- the so called  double blind study.
I don't know the details of their study but if they did not know and/or control the nutritional status of their subjects there could by chance be  nutritional deficiencies which  could give them their correlative findings-  the scenario being that the exercise group  were not deficient while the control group was .We need to know the nutritional status of vitamin C in their study.?
 Why is it important ? Because it is known that this water double vitamin besides being an anti-oxidant (free radical scavenger ) it is also an important nutrient  involved in collagen synthesis- the most common protein in our body. In severe Vit. C deficiencies  like those experienced by sailors in the days of sailing ships on their long sea journeys  or with the early explorers into regions with long winters where no fresh fruits and/or  vegetable were available, a deficiency of Vit C could cause symptoms of scurvy and in many cases even death; Recently some scientists have  noted skin rejuvenation following Vitamin C cream applications to the skin.
 In one of my earlier blogs I mentioned  the finding that low serum levels of Vitamin D were found in those patients diagnosed  with Alzheimers, autism, and Parkinson's, indicating the importance of knowing the nutritional status of subjects in their clinical trials
Question remains if the investigators did not determine the nutritional status of both groups then it is possible by chance that the diet of all those who exercised happened to belong to the well supplemented  Vitamin C group, while  the control group was not ?