The role of vitamin D

Vitamin D has many roles in the body, including bone metabolism, cell growth modulation, neuro-muscular and immune function, and inflammation reduction. However, further investigation is needed to determine whether healthy levels of vitamin D can reduce the risk of non-skeletal diseases. The role of vitamin D in multiple sclerosis, autoimmune disorders, infections, rheumatoid arthritis, respiratory disease, cardio-metabolic disease, cancer, and fracture risk is still being studied.

Dietary vitamin D is absorbed in the small intestine and then transported to the liver. From the liver, vitamin D travels to the kidney, which converts vitamin D to its most active form. Sunlight also helps activate vitamin D, so it is no surprise that we currently have a vitamin D deficiency epidemic as we spend most of our time inside, away from the sun.

Dietary sources of vitamin D include fatty fish (salmon, tuna, sardines, swordfish), cod liver oil, egg yolks, portabella mushrooms, beef liver, and fortified foods such as breakfast cereal, milk (dairy and nondairy), infant formula, cheese, and orange juice. Fortified foods in the United States use synthetic vitamin D₂ (ergocalciferol) derived from irradiation of ergosterol found in plants, mold ergot, or plankton. Vitamin D3 (cholecalciferol) is more effective than vitamin D2 in maintaining adequate vitamin D levels in the blood.

The Institute of Medicine recommends 600 IU of vitamin D per day to meet the needs of most people aged 1 to 70 years. Those older than 70 years may need 800 IU per day,²¹ assuming minimal sun exposure. The Endocrine Society recommends 1500 to 2000 IU per day for adults and 1000 IU for children.¹⁸ Vitamin D should be given with calcium to maintain bone health in those who are deficient.  All adults found to be vitamin D deficient should be treated with either 50,000 IU of vitamin D₃ per week or 6000 IU per day for 8 weeks to achieve a serum 25(OH)D level of 30 ng/mL. The American Academy of Pediatrics recommends that all children receive 400 IU per day of vitamin D from their first few days of life through adolescence.

In a 2014 report, the American Geriatrics Society recommended vitamin D supplementation of 1000 IU per day or more plus calcium for all adults aged 65 years or older to reduce the risk of fracture and falls. But the Endocrine Society did not recommend vitamin D supplementation for the sole purpose of fall risk reduction.

Vitamin D is fat-soluble, meaning that it cannot be excreted by the body, and can reach toxic levels in your blood if you were not deficient to begin with. Please consult your doctor before starting any vitamin D supplementation. For patients taking vitamin D supplements for deficiency, routine laboratory testing is not recommended as long as the prescribed dose is within the recommended limits.