Vitamin D

Vitamin D, also known as the “sunshine” vitamin, was first isolated in 1930 and named calciferol. Today, the two major forms of this fat-soluble vitamin are vitamin D₂ (ergocalciferol), found in plant sources, and vitamin D₃ (cholecalciferol). The action of the sun’s ultraviolet rays on the skin forms vitamin D in the body. It is responsible for regulating calcium and phosphorous levels in the blood by promoting their absorption from food in the intestines, and subsequent reabsorption of calcium in the kidneys.

In addition to supporting bone formation and mineralization, it impacts the immune system by elevating phagocytosis, antitumor activity, and immunomodulatory functions. Recently, new evidence has come to light that suggests vitamin D plays a role in neuromuscular functioning in older adults, and this role may have an effect on both functional performance and the risk of falls among this demographic. New studies are also looking at its potential ability to reduce the risk of many common concerns and autoimmune diseases related to diabetes, hypertension and age-related muscle weakness. No one is yet suggesting that this vitamin will prevent or cure all these disorders, or advocating that everybody take supplements, but the research is promising.

D deficiency

Diseases, such as rickets, can develop if the serum ion product of calcium and phosphorous is not maintained at a level consistent with normal bone mineralization. Insufficient deposition of calcium phosphate into the bone matrix creates bones that are not strong enough to withstand the ordinary stresses and strains of weight. In adults, vitamin D deficiency can result in osteomalacia and osteoporosis.

Vitamin D deficiency can result from inadequate dietary intake, insufficient exposure to sunlight, which reduces the body’s synthesis of vitamin D, and kidney or liver malfunctions, which inhibit the conversion of vitamin D to its metabolically active forms. Additionally, gradual hearing loss can occur because demineralization of the bones in the middle ear inhibits the transmission of vibrations to the nerves that communicate sound waves to the brain. Vitamin D deficiency also causes muscle weakness, severe tooth decay and phosphorus retention in the kidneys.

Levels for fortification

Most people don’t consume enough vitamin D unless they drink lots of milk or take a multivitamin. Currently, the recommended intake is 200 international units (IU) per day for young adults; 400 IU per day for ages 51 to 70; and 600 IU per day day for those over 70 years old. However, many researchers believe those guidelines are too low and that a better goal for everyone, especially for those over 60 and/or with darker skin, is 800 to 1,000 IU per day. These recommendations are based on the amount of vitamin D intake needed to maintain a serum 25-hydroxyvitamin D concentration that will maintain suppressed levels of serum parathyroid hormone (PTH), which is associated with increased bone resorption and loss. Because PTH can be affected by a number of factors, such as diurnal rhythm, calcium intake, renal function and physical activity, estimates of optimal serum 25-hydroxyvitamin D to achieve PTH suppression have varied widely between studies, making consensus difficult.

Vitamin D₃ is typically used in fortification of foods, as it is more stable due to one less double bond.

Ram Chaudhari, Ph.D., FACN, CNS, is senior executive vice president and chief scientific officer, Fortitech, Schenectady, NY. For more information, log on to fortitech.com, or e-mail info@fortitech.com.