Healthy vitamin D blood levels for adults fall between 20 nanograms/milliliter to 50 ng/mL. Levels under 12 ng/mL signal a vitamin D deficiency, reports WebMD. Levels of vitamin D higher than 50 ng/mL may cause side effects, according to Mayo Clinic.
As of July 2015, the recommended daily allowance, or RDA, for vitamin D is 600 IU per day for children and adults between the ages of 1 and 70. The RDA for adults 71 and older is 800 IU, and infants under 12 months require 1,000 IU per day, states Mayo Clinic.
Low levels of vitamin D in the body can result in brittle, thin or misshapen bones, according to Mayo Clinic. Additionally, a vitamin D deficiency is also associates with increased risks for autoimmune diseases, osteoarthritis, depression, cardiovascular disease and cancer, notes Healthline. Other conditions linked with vitamin D deficiency include type 1 diabetes and multiple sclerosis.
Although most people with low levels of vitamin D don't exhibit any symptoms, potential symptoms of vitamin D deficiency include muscle weakness, bone pain, joint pain, depression and fatigue, according to Healthline. People who avoid the sun, vegetarians and adults over the age of 65 are at increased risk of vitamin D deficiency.