A deficiency of vitamin D in the body can lead to brittleness, warping and thinness in the bones. While vitamin D may also help with hypertension, immune function and insulin resistance, those connections require further research, according to Mayo Clinic as of February 2015.
For adults, the recommended dietary allowance is 600 IU of Vitamin D per day. After people turn 70 years old, that requirement goes up to 800 IU each day. With most adults, a deficiency in vitamin D is not a problem because, even though the dietary vitamin D that adults ingest with their diet is generally less than the recommended amount, spending time in the sunlight can compensate for that gap. However, people with darker skin and people over 65 might not get enough vitamin D either through diet or through sunlight exposure, according to Mayo Clinic.
While supplements of vitamin D are available, choosing certain foods that are rich in this vitamin is also helpful. Milk and yogurt are available with vitamin D added, and such fatty fish as trout, salmon, halibut and tuna are also rich in vitamin D. Because different people have different dietary needs, the Mayo Clinic advises individuals to discuss this issue with a physician before bone damage occurs if an examination indicates low vitamin D levels.