Vitamin D: Over the past decade, dozens of studies have revealed many important roles for vitamin D, the nutrient that skin cells produce when they are exposed to sunlight. The recommended daily intake of Vitamin D is 600 IU per day, although recommended levels are under review. If you avoid the sun or live in the northern half of the U.S., ask your doctor whether your vitamin D level should be tested.
If motivation is your hang-up, change your exercise routine every 14 days. A University of Florida study discovered that people who modified their workouts twice a month were more likely than to stick to their plans compared to those who changed their regimens whenever they wanted to. Boredom didn’t appear to be a factor; it seems people simply enjoyed the variety more.