Sunlight & Liver Function

Sunlight allows the skin to produce vitamin D.

Mosby's Medical Dictionary explains that the liver has more than 500 determined functions. Primarily the liver functions as a gland, releasing bile and other enzymes and hormones to the body. The liver is also a site of detoxification of substances such as alcohol and many medications.

Sunlight and Vitamin D

According the Linus Pauling Institute at Oregon State University, vitamin D is synthesized in the skin when the skin is exposed to direct sunlight. The vitamin D produced in the skin is then transported to the liver, where it is converted to its active form. Vitamin D is essential for the proper metabolism of calcium in the body. Calcium is important for nervous system functioning and the building and maintenance of bones. Activated vitamin D increases the absorption of calcium from foods in the intestine and the reabsorption of calcium from the urine in the kidneys. Vitamin D is also able to mobilize calcium from bones when the available calcium in the blood is low. A deficiency of vitamin D can lead to rickets, osteomalacia, or soft bones, and muscle weakness and pain.

Jaundice

The University of Michigan Health System describes jaundice in newborns as caused by an immature liver. Red blood cells are naturally broken down in your body as they age. A byproduct of this breakdown is bilirubin. Bilirubin is normally removed from the bloodstream by the liver. In an immature or damaged liver, bilirubin may begin to build up in the bloodstream and collect under the skin, causing the yellow skin and eyes associated with jaundice. The treatment for jaundice in newborns is made up of two parts. First, frequent feedings are ordered, as the bilirubin is excreted in the feces. Secondly, phototherapy is given, either in the form of natural sunlight or a biliblanket. The sunlight breaks down the bilirubin in the body, allowing it to be more easily removed.

Sunlight as a Cause of Liver Damage

In "International Hepatology Communications," author Rumi Ghosh describes a study of sunlight exposure in which rats were exposed to intense sunlight every day for 12 weeks for either one or two hours per day. At both exposure times, many liver enzymes were elevated. With two hours of exposure per day, spotty necrosis of the liver was visible under the microscope, indicating the exposure to sunlight had caused damage to the liver.

Erythropoietic Protoporphyria

Erythropoietic protoporphyria is sensitivity to sunlight caused by a building block of red blood cells. Merck Manuals describes the condition as intense pain and swelling of the skin when exposed to sunlight. The condition usually appears in childhood. The cause of the disorder is the absence of the enzyme that allows a build-up of a protoporphyrin, a precursor to heme---a component of hemoglobin. Protoporphyrin collects in the bone marrow, blood plasma, red blood cells, skin and the liver. When exposed to sunlight, protoporphyrin is activated, causing damage to the surrounding tissue. This can lead to liver failure, jaundice, pain and an enlarged spleen. With severe damage to the liver, a transplant may be necessary. The only known treatment for erythropoietic protoporphyria is avoidance of the sun. In some patients, beta-carotene taken in amounts high enough to tint the skin yellow provides some protection.

Hepatogenous Photosensitization

According to the Purina website, the liver is a resilient organ, able to function normally with up to 80 percent of the organ damaged. After that point, animals will begin to show symptoms. In horses and other animals that feed mainly on plants, hepatogenous photosensitization may develop. This occurs when the liver is damaged to an extent that it can no longer remove the substances produced from the breakdown of chlorophyll in green plants. These substances accumulate in the blood. In the presence of sunlight, these chlorophyll-based substances fluoresce, causing damage to the skin. This skin damage then leaves the animals sensitive to sunlight.

References

• "International Hepatology Communications" journal: "Sunlight exposure: a possible cause for hepatocellular injury"; Rumi Ghosh; February 1996
• University of Michigan Health System: Your Baby, Jaundice, and Phototherapy
• Oregon State University, Linus Pauling Institute: Vitamin D
• Merck Manuals: Erythropoietic protoporphyria
• Purina: Liver Disease Inducing Plants

Resources

• "Mosby's Medical, Nursing, and Allied Health Dictionary", Fifth Edition; 1998