Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts ), long-distance travel, and the influence of universal indoor lighting.  Even if they have sleep debt, or feel sleepy, people can have difficulty staying asleep at the peak of their circadian cycle. Conversely they can have difficulty waking up in the trough of the cycle.  A healthy young adult entrained to the sun will (during most of the year) fall asleep a few hours after sunset, experience body temperature minimum at 6AM, and wake up a few hours after sunrise. 
The primary reason for baseline deficiencies in both the general population and in serious athletes is that it's difficult to get proper amounts of zinc and magnesium solely through diet alone. USDA studies show that 68% of self-selected diets contain less than two-thirds of the RDA for zinc  and 39% contain less than two-thirds of the RDA for magnesium.  While zinc and magnesium are contained in a wide variety of foods, it's been my experience that athletes don't acquire sufficient quantities through their normal diets. One reason may be that foods high in these minerals aren't necessarily the most desirable. For example, the best food sources for zinc include oysters and beef liver. These foods aren't consumed by most athletes, nor should they be.