What is vitamin D?
The "sunshine" vitamin is a hot topic.
Should people be exposed to the sun for their vitamin D? Are the
guidelines for how much vitamin D we need adequate? Is the tolerable
upper limit too low? What benefits does vitamin D have on our health?
This article will discuss and respond to all of these common questions.
There
are two forms of vitamin D, known as D2 and D3. Vitamin D2, also known
as ergocalciferol, comes from fortified foods, plant foods, and supplements.
Vitamin D3, also known as cholecalciferol, comes from fortified foods,
animal foods (fish, eggs, and liver), and can be made internally when
your skin is exposed to ultraviolet (UV) radiation from the sun. Vitamin
D is a fat-soluble vitamin. This means that it is stored in our fat
cells for use when it is needed. It is constantly being used for calcium
metabolism and bone remodeling.
What is vitamin D? (Continued)
The guidelines for how much
vitamin D we need were updated in 2010 by the Institute of Medicine
(IOM). They were set based on the evidence for bone health and assumed
that there was limited sun exposure. The recommended dietary allowance
(RDA) for vitamin D is as follows:
- 600 IU/day for ages 1 to 70
- 800 IU/day for over 70 years of age
- 600 IU/day for pregnant and lactating women
These
recommendations have been met with a lot opposition by some experts,
saying that they are too low. The evidence review that the IOM did was
based on 1,000 studies. They were limited by the types of studies and
availability of studies to support the benefits linking vitamin D to multiple sclerosis, heart disease, cancer,
By the turn of the 20th century, most of the children living in New
York, Boston, and Leyden in the Netherlands were afflicted with rickets,
a bone-deforming disease. The first observation of this disease was in
the mid-1600s by Whistler and Glissen, who reported that children living
in industrialized cities in Great Britain had short stature
and deformities of the skeleton, especially of the lower legs. It
wasn't until 1889 that the discovery that "sunbathing" was important for
preventing rickets came about.
The need for vitamin D goes way
beyond preventing and treating rickets. Various researchers have claimed
that vitamin D benefits are associated with the following:
- Prevention of osteoporosis and osteopenia
- Lowering blood pressure in people with hypertension
- Lowering incidence and severity of cardiovascular disorders
- Decreasing the incidence of type 2 diabetes: Research has shown that those with blood vitamin D levels over 25 ng/mL had a 43% reduced risk of developing type 2 diabetes compared with those with levels under 14 ng/mL.
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