Although the amount of vitamin D adults get from their diets is often less than what's recommended, exposure to sunlight can make up for the difference. For most adults, vitamin D deficiency is not a concern. However, some groups — particularly people who are obese, who have dark skin and who are older than age 65 — may have lower levels of vitamin D due to their diets, little sun exposure or other factors. The Recommended Dietary Allowance (RDA) for adults is 600 international units (IU) of vitamin D a day. That goes up to 800 IU a day for those older than age 70. To meet this level, choose foods that are rich in vitamin D. For example, choose fortified foods, such as milk and yogurt, and fatty fish, such as salmon, trout etc...within few month's you can get back your levels to normal.. you can take vitamin D syrups and sachets to increase your vitamins levels....consult your doctor they will help you