According to vitamindcouncil.org, vitamin D deficiency throughout life can play a major role in the pathology of many varieties of cancer, heart disease, autoimmune diseases, diabetes, osteoarthritis, osteoporosis, muscle weakness, muscle wasting, and birth defects.
Vitamin D is crucial for strong bone development and maintenance throughout life. Deficiency can lead to rickets in children, a bone softening disease that can result in bowed legs and fractures. To prevent this deficiency, The American Academy of Pediatrics recommends that children get at least 400 international units (IU) of vitamin D a day, and that blood levels not fall below 50 nanomoles per liter (nmol/L).
Sunlight is the best natural source of Vitamin D. However, for infants and children, diet and supplementation are the main sources of Vitamin D because this age group does not produce enough Vitamin D from sun exposure. A main reason for this is constant use of sunscreen, an important precaution against skin cancer. For infants, formulas and liquid supplements are the main source of Vitamin D until the child begins to consume dairy and raw fruits and vegetables.
Infants: both breast-feeding and formula fed should be given a vitamin supplement of 400 IU each day.
Toddlers and Children: 400 IU each day in addition to a well-balanced diet..
Foods High in Vitamin D:
Milk (25% or 98 IU in one 8 ounce glass)
Fortified Cereals (10% in one cup cheerios)
Cheese (12 IU per slice)
Fish (360 IU in 3.5 ounces salmon, mackerel)
Cod Liver Oil (1360 IU in 1 tablespoon)
Eggs (20 IU in whole egg)