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It seems like practically every week, I read a study about how vitamin D might be related to another disease process. There is still a lot to learn about this complex chemical.
Vitamin D is a fat-soluble vitamin made up of two molecules: ergocalciferol (D2) and cholecalciferol (D3). Ultraviolet B (UVB) light is absorbed by the skin and converts 7-dehydrocholesterol to vitamin D3. Also, vitamin D2 and vitamin D3 are part of our diet, especially from fortified milk, fatty fish (like salmon or cod liver oil), and fortified cereals. Both vitamin D from the sun and the diet enter the liver to be converted to 25-hydroxyvitamin D (calcidiol), which is the major circulating form of vitamin D. This is used to determine vitamin D status.
According to recent research and recommendations from vitamin D experts, ideal blood serum levels are between 30 and 60 ng/mL. Insufficiency is 25 to 30 ng/mL. However, rickets or osteomalacia may be evident at less than 20 ng/mL, and frank insufficiency is less than 10 ng/mL. (These numbers may vary slightly from lab to lab.)
One more chemical reaction takes place in the kidneys to form active 1,25-hydroxyvitamin D (calcitriol), which is the active form of vitamin D that is broken down in a matter of hours after being formed.
The calcitriol form of vitamin D acts as a hormone and is important in the function of intestine, bone, and kidney that result in the maintenance of plasma calcium, phosphorus, and magnesium.
Vitamin D deficiency can occur when people do not get enough UVB rays or do not eat enough vitamin D. According to the National Institutes of Health (NIH), 10 to 15 minutes of direct sunlight at least twice a week to the face, arms, hands, or back is enough to maintain normal vitamin D levels. However, sunscreen and low outdoor sun exposure can result in inadequate production of vitamin D in the skin.
In fact, there are varying opinions on whether or not sunscreen can be a primary cause of vitamin D deficiency. Studies have shown that SPF 8 decreases vitamin D production by 92.5 percent and SPF 15 by 99 percent.
People with darker skin also have a reduction of vitamin D production by up to 99 percent because the UVB rays are being absorbed by the skin pigment, melanin. There is a reduction of the chemical that becomes vitamin D in the skin of older people, such that only 25 percent of vitamin D3 is produced in a 70-year-old. Therefore, people with darker skin and the elderly need to eat more vitamin D than average.
Because the sun does not rise high enough in the sky in the winter months, people who live in high latitudes must eat more vitamin D3 and D2. It has been shown that above 35 degrees north latitude (Atlanta), little or no vitamin D3 can be produced from November to February.
The use of tanning beds has been discussed as an option for increasing UV exposure and, in turn, increasing vitamin D levels. While tanning beds can result in vitamin D photosynthesis, they also increase the incidence of skin cancer and photo aging. Therefore, due to the damaging effects of UVB radiation from artificial sources, it is not recommended that people use tanning beds as a main source of vitamin D.
Vitamin D is fat-soluble and therefore easily stores in adipose tissue, which results in decreased vitamin D in the bloodstream. It has also been found that release of vitamin D from the skin into circulation is decreased in obese women. Due to this information, people who are obese should try to obtain more vitamin D from their diet.
Recommendations from 1997 for vitamin D intake were 200 IU/day for young adults, 400 IU/day for ages 51 to 70, and 600 IU for those greater than 70 years of age. However, it has been shown that maintenance of adequate serum levels of vitamin D requires higher daily intake. Through current research, it has been determined that the average recommended supplement intake is 1000 IU of vitamin D daily for all ages.
Vitamin D supplements are relatively safe. To reach vitamin D toxicity, the serum level needs to be at 150 ng/mL or above. This serum level would likely require supplementation greater than 10,000 IU per day.
Next week, I will write about the problems that may be related to not having enough vitamin D circulating in your blood. In the meantime, do as your mother told you. Drink your milk. Then go outside and get some sun. That way, you will avoid needing to drink some cod liver oil.
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