Skin is the body's largest organ system. It functions as the primary protective device of the body. Receptors in skin protect the body from heat and cold. Skin layers protect it from dehydration and physical injury and sweat glands excrete wastes. Importantly, it contains a vitamin D precursor, which is converted to vitamin D by sunlight. It is the only way the body can create vitamin D, a required nutritional element. Not many foods contain natural vitamin D.
Vitamin D
Vitamin D has two forms: Vitamin D2 existing in plants and D3, cholecalciferol, produced by the skin upon UV exposure. Vitamin D3 is essential for normal bone growth and development. The vitamin assumes an important role in the maintenance of blood of calcium and phosphorus, which supports normal mineralization of bone. Most cells in the body have a vitamin D receptor, which is responsible for genes that regulate cellular processes and immonomodulation.
Skin
Skin forms three layers: epidermis, dermis and hypodermis. UV radiation from the sun penetrates the deepest layers of the epidermis, converting pre-vitamin D3 to usable vitamin D3. The process of reaching maximum D3 production can take 20 minutes in light-skinned individuals and three to six times longer in dark-skinned individuals. Overexposure of skin to sunlight will not cause toxicity; the body only produces what it needs.
Nutrition
Very few foods contain natural or supplemented vitamin D. A diet high in oily fish gives sufficient vitamin D; supplemented foods include cereal, milk, energy bars, eggs, meats and some soups. The Institute of Medicine and Health Canada recommends a vitamin D3 daily intake of 200 international units (IU) per day for children and adults up to 50 years old. Requirements double for adults over 50 at 400 IU per day.
Psoriasis
Psoriasis is a chronic disease characterized by inflamed lesions covered with dead skin. In this disease, skin cells mature faster than normal and the body cannot shed the dead cells fast enough. The cause of psoriasis is unknown, but it appears that immune system malfunction triggers the disease. Research linking vitamin D to skin's immune system in journals such as the Journal of Investigative Dermatology support its use as a treatment for psoriasis.
Atopic Dermatitis
Atopic dermatitis covers multiple conditions that cause itchy, inflamed rashes. Persistent rashes increase the risk of skin infections, a common complication. The symptoms usually occur in children and young adults with no effect on general health. This condition is thought to be an inherited over-active immune system and since vitamin D has been linked to the skin's immune system, vitamin D treatment can help alleviate symptoms.
Cancer
Basal cell carcinoma is the most common form of skin cancer, affecting the deepest layer of the skin. In a study at Henry Ford Health System in Detroit, researchers linked basal cell carcinoma with elevated vitamin D levels in the affected tissues. Also, genes that play a role in tumor repair had elevated levels of vitamin D in cancerous tissues. Other research expands vitamin D’s involvement with complex cellular pathways, showing promise toward preventing and treating skin cancer. Therefore, UV light, which creates usable vitamin D, may actually help fight cancer.
Age
Dermal production of vitamin D following exposure to UV light decreases with age because of skin changes, which reduce the amount of pre-vitamin D within the epidermis. Also, sun exposure is usually limited due to lifestyle changes, such as clothing and outdoor activity. These changes render the aging population at risk for vitamin D deficiency. Vitamin D supplementation proved to decrease falls in elderly, thus reducing the incidence of broken bones.
References
- The New England Journal of Medicine: Vitamin D Deficiency
- The Society for Investigative Dermatology, Inc.: Sunlight, Vitamin D, and the Innate Defenses of the Human Skin
- Henry Ford News: Study Shows Link Between Vitamin D, Skin Cancer
- The Free Dictionary: Atopic Dermatitis
- The Free Dictionary: Psoriasis
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