We used to spend a lot more time outside, but for the majority of us, the nature of our modern lifestyles keeps us out of the sun. As a result of this, vitamin D deficiency is extremely common, studies show that 1 in 3 Canadians is deficient, and 2 in 3 have less than the recommended level. Vitamin D deficiency can manifest itself in symptoms like low immune function, fatigue, muscle weakness, mood imbalances, and osteoporosis in older adults.