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Tuesday, March 11, 2014
Most people know that being exposed to the sun's rays can be harmful (it can increase the risk of skin cancer), but they may not know there's a risk of too little sun.
Sun exposure is actually beneficial when obtained in small doses-such as 15 minutes or less several times a week. The sun's ultraviolet rays actually trigger vitamin D synthesis in the skin. Vitamin D is important because it helps us absorb calcium from the digestive system for our bones.
The days are getting shorter as winter approaches, and people are less exposed to the sun. Even if they are getting sun exposure, the winter sun is too weak to be beneficial.
A vitamin D deficiency prevents new bone tissue from hardening, a condition known as rickets in children and osteomalacia in adults. It can also result in bone loss and causes muscle weakness, which creates an increased tendency to fall.
Research studies have also found that insufficient levels of vitamin D may also contribute to developing different types of cancer such as breast, colon and prostate cancer, as well as heart disease and diabetes.
Here's what you need to know about vitamin D:
Vitamin D is a fat-soluble vitamin found in some foods and which can be made in your body after exposure to ultraviolet rays from the sun.
Breastfeeding infants-Human breast milk alone doesn't provide adequate vitamin D, and parents are advised to keep infants out of the sun. So the Academy of Pediatrics recommends a daily supplement of 400 international units (IU) of vitamin D per day beginning at age 6 months, unless they are weaned to receive at least 500 ml per day of vitamin D-fortified formula.
Older adults-The skin of adults aged 50 and older does not synthesize vitamin D efficiently and the kidney is less able to convert vitamin D to its active hormone form.
People with darker skin color-The melanin content is higher in people with darker skin, which reduces the skin's ability to produce vitamin D from sunlight.
People with fat malabsorption-Because vitamin D is a fat-soluble vitamin, people with a reduced ability to absorb dietary fat, such as those with Crohn's disease, cystic fibrosis, celiac disease or liver disease, or those who have had part or all of their stomach or intestines removed (as a result of gastric bypass surgery, for example), may not adequately absorb vitamin D.
People with limited sun exposure-Homebound individuals, people living in northern latitudes like New England and Alaska, and those who wear more protective clothing are at risk for vitamin D deficiency.
The current recommendations are: from birth to age 50, people should get at least 200 IU of vitamin D a day. Adults 51–69 require 400 IU daily, and those over 70 require 600 IU. Many experts in the field recommend 1000 to 2000 IU per day and some patients need more.
The 'safe upper limit' for vitamin D is 2,000 IU per day, and higher levels may be needed for some people. Although there is a wide margin of safety, taking too much vitamin D can lead to toxicity, which through high blood calcium levels can cause nausea, vomiting, poor appetite, constipation, weakness and weight loss. It can also cause heart rhythm abnormalities and confusion."
Exposure to the sun provides most people with their vitamin D requirement, because ultraviolet rays trigger synthesis in the skin.
However, the sun's rays are not strong enough in the winter and there are other ways to get vitamin D. There are some foods that contain vitamin D, such as egg yolks, sardines, mackerel, salmon, herring, fish liver oils, shrimp, chicken liver, oysters and fortified foods such as orange juice, milk and infant formula.
It's difficult to get your daily recommended amount from foods containing vitamin D, and most multivitamins only contain 400 IU of vitamin D, so most people will need an additional supplement.
This article originally appeared in UC Health Line (12/06/05), a service of the University of Cincinnati Academic Health Center Public Relations Communications Department and was adapted for use on NetWellness with permission, 2006.
Last Reviewed: Dec 29, 2008
Nelson Watts, MD, FACP, MACE
Professor of Medicine
Director, Bone Health and Osteoporosis Center
College of Medicine
University of Cincinnati