Protein timing is a crucial element of exercise recovery. Which protein you use and when you use it can have a noticeable impact on muscle size and strength gains. A study presented at The Endocrine Society's 95th Annual Meeting in San Francisco suggests that vitamin D and calcium timing effects bone adaptation to training in a similar way.
Researchers had 52 male volunteers ranging in age from 18 to 45 supplement their diet with 1,000 mg of calcium and 1,000 IU of vitamin D. Some took the combination 30 minutes before participating in a simulated 35 km cycling event while others took the supplements 30 minutes after completing the task.
Although the results were inconclusive, scientists theorized that pre-workout calcium might help stabilize blood sugars during exercise. As levels of calcium in your bloodstream decrease, hormones are produced that move calcium from the skeleton. This process may contribute to exercise-induced bone loss. It's possible that pre-workout calcium and vitamin D supplementation could slightly decrease the effect during endurance exercise.