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Dear Dr Denton: Does sun- block somehow affect Vitamin D in the body? Yes.

PORTSMOUTH, VA. (Catholic Online) - Sun - blocks prevent penetration of light waves from stimulating the transition of cholesterol (cutaneous 7-dehydrocholesterol) to Vitamin D in the body. Even though we worry about the potential risks of sun exposure, what about our need for Vitamin D and its benefits?

Vitamin D is a fat-soluble vitamin that acts more like a hormone than a vitamin. Vitamin D can come from food, but is largely made in the body after ultraviolet light (sunshine) stimulates the conversion of cholesterol type compounds to become Vitamin D. The Vitamin D then goes through two modifications in the liver calcidiol - (25-hydroxyvitamin D) = 25(OH) D)- and the kidneys, where it becomes activated.

The active Vitamin D is called calcitriol - (1.25-dihydroxyvitamin D) = 1.25(OH)2D.). Once activated the Vitamin D sticks around for 15 – 20 hours (half-life 15 hours). Think of it this way single numbered Vitamin D 25 on the team is the storage guy, once he gets the #1 put on his chest - 1.25(OH)2D - he gets his confidence up and starts getting active telling the body what to do. Simply put, sunshine hits our skin and it all begins to happen. The skin converts some type of cholesterol to form Vitamin D. This Vitamin D has to go to the liver and then the kidneys to become a form of Vitamin D that is useful to the body.

In addition, Vitamin D is largely known for its bone function. By promoting calcium absorption from the gut, Vitamin D stabilizes the serum levels necessary for normal muscle and bone function. Approximately 99% of this calcium goes into bone. The remainder plays a role in cell membrane bioelectrical balance, the electrical charge across a cell membrane allows the cell to gain nutrients and rid itself of waste. The mineralization of bone is largely modulated via Vitamin D and its effects on osteoblasts and osteoclasts. These are both little cells that make and remove bone.

A lack of Vitamin D leads to brittle and thinned bone. Calcium and Vitamin D combine to protect us from these bone diseases (i.e. osteoporosis). Although rarely mentioned, Vitamin D has beneficial effects on immune function, inflammation reduction, and cell proliferation/death.

When testing for Vitamin D deficiency, the storage level is measured, not the active form in the system. This is because the storage form is a better measure of the bodies overall Vitamin D levels. "Rickets disease" is the most common terminology used for Vitamin D deficiency. It is often seen in children. For example, soft long bones leading to bowed legs.

One of the most confusing things about nutrition is the challenge of understanding the terminology used for what we need daily to live beautiful healthy lives. Dietary Reference Intakes (DRIs) is the term used for a set of reference values used to determine nutrient intakes to sustain healthy humans. These reference values are the Recommended Dietary Allowance (RDA), Adequate Intake (AI), and Tolerable Upper Intake Level (UL). You will see these letters in multiple articles as well as on food containers.

• Recommended Dietary Allowance (RDA): daily level of intake sufficient to meet the nutrient requirements of (97-98%) healthy people.
• Adequate Intake (AI): when an RDA cannot be set because of insufficient data the AI is set at a level assumed to ensure nutritional adequacy.
• Tolerable Upper Intake Level (UL): maximum safe daily intake

Another confusing part about vitamins and the dosing is the amount listed can be in micrograms, milligrams, or even international units. The Adequate Intake (AI) for Vitamin D is listed in either micrograms (mcg) and or International Units (IUs). 1 microgram is equal to 40 IUs. The Adequate Intake levels were established with the assumption that the individual is not producing vitamin D through sun exposure.

Reference Intakes:

The chart in the box included to the side of this article represents the “Adequate” intakes for Vitamin D. Knowing these daily requirements is only part of the battle we face to assure that we have the appropriate levels of Vitamin D. So how do we get Vitamin D into our bodies?

SUN, SUN, SUN, oh HAPPY SUN.

WAIT A Minute… didn’t I just write an article on sun protection? Once again, the balance of too little and too much becomes clear. O.K. you may ask, but how about some guidelines?

Most people get their Vitamin D from the sun. Sunlight above the 42 degrees N. latitude (Northern California – Boston) from March through October will have enough intensity to give you a Vitamin D dose. The other four months are a problem. 34 degrees N. (L.A. to Charleston S.C.) and below has an intensity of sun to give the body enough Vitamin D year around.

Shade reduces UV energy by as much as 60%. UVB doesn’t pass through glass so Vitamin D doesn’t get ...