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(NewsTarget) The first part of this article began a series of questions and answers aimed at introducing vitamin D and describing its importance to health. This part continues the series with a focus on sources of vitamin D, along with information on appropriate dosing.The body can make its own vitamin D following exposure to UVB radiation from the sun. Adequate exposure typically requires around 15 to 20 minutes of midday sunlight, 2 to 3 times per week. However, this particular ultraviolet light is not available during the winter months at some latitudes, while other latitudes offer a year-round supply. The greater the distance from the equator, the less UVB there is. Another factor to consider when it comes to sun exposure is skin pigmentation. Those with darker skin will require a longer duration of exposure to sunlight, compared to those with lighter skin.Remember to protect your skin if you are going to be in the sun for prolonged periods of time. Sensible sun exposure must be balanced against the harmful effects of sunburn.Supplementation can provide an optimal amount of vitamin D for those unable to spend sufficient time in the sun. There are also dietary sources of vitamin D, but it's practically impossible to get enough from food alone. Some examples include fatty fish, egg yolks and fortified milk. To reach even bare minimum levels would require drinking around 20 glasses of milk every single day.The two forms of vitamin D available as supplements are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Fungi, plants and invertebrate animals make ergocalciferol. Cholecalciferol is produced in the skin of vertebrate animals, including humans. There is only a slight difference in molecular structure between these two compounds. Still, that small difference has a significant impact on biological activity. In humans, vitamin D3 is much more effective, and safer, than vitamin D2. Therefore, if you supplement, be sure that you are taking vitamin D3, or cholecalciferol.Estimates from current research show that a healthy individual uses around 4,000 IU of vitamin D per day. The dose needed to satisfy daily demand varies depending upon sun exposure factors, age and weight. Generally, older people need more than younger people, and those who are overweight need more than those who are normal weight.Fortunately, there is a wide gap between the level of supplementation that will guarantee optimal vitamin D status and the level that could lead to toxicity. Research has shown that vitamin D toxicity may occur following long-term intake of around 40,000 IU daily; whereas, toxicity is unlikely with a daily intake of 10,000 IU or less. While it is true that most individuals do not need a dose of 10,000 IU per day, it's good to know that vitamin D has such a wide margin of safety.The only way to be certain of vitamin D status is to measure the blood level of 25(OH)D, also known as calcidiol. Experts recommend having at least one test every year. It is also advisable to check a few months after beginning regular supplementation, especially when taking 5,000 IU per day or greater. Additionally, anyone taking extremely high doses for an extended period should be aware of the signs and symptoms of vitamin D toxicity. These may include nausea, vomiting, poor appetite, constipation, weakness, kidney stones, and arrhythmias, along with elevated blood levels of calcium, liver enzymes or cholesterol.Vitamin D CouncilDr. Michael F. Holick on Vitamin DWikipedia, "Vitamin D"GrassrootsHealthSunlight, Nutrition And Health Research CenterJeremiah Smith is a licensed and practicing pharmacist with a strong interest in nutrition and natural medicine. He is driven by a thirst for knowledge and a passion for helping others achieve optimal health . Smith writes articles on a range of topics related to wellness. You can visit his website at ( http://www.anewvision.info/