‘VITAMIN D’ FOR BONE HEALTH AND RESPIRATORY HEALTH

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Experts have defined vitamins as organic bio-chemicals that play a crucial role in our body's metabolism, which can be obtained from dietary sources alone because they are not produced by our body. Also to be noted that only tiny amounts of vitamins are needed to fill that role.  
Now concentrating on Vit D which is one of the four fat-soluble vitamins, it is not technically a vitamin. True, it's essential for health, and only minuscule amounts are required because it's produced in the human body, it's absent from all-natural foods except for fish and egg yolks that have D3, whereas mushrooms are the only good plant source but produce very little of vitamin D2. Like humans, mushrooms can synthesize this vitamin when exposed to UV light (now there are fortified ones too). Even though both are obtained from foods, it must be transformed by the body before it can do any good. Also to be noted vitamin D2 is not as effective as vitamin D3.
(Vitamin D is a fat-soluble vitamin that exists in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).)
As our lifestyle has changed, most of us cannot rely on our bodies to produce vitamin D the old-fashioned way (sun). Instead, we increasingly depend on artificially fortified foods and supplements to provide this vital nutrient thus fitting into the technical definition of a vitamin.    
WHAT IS VITAMIN D???
Your body needs vitamin D. Its main job is to help the body absorb calcium from the intestines. This calcium is necessary to help “mineralize the skeleton” over the course of your lifetime and is a critical mineral for forming the hardened bone that keeps you strong and healthy.
Vitamin D is not one chemical or process but a chain of reactions. The natural type is produced in our skin’s cholesterol i.e. 7-dehydrocholesterol. Sunlight is the key. Its ultraviolet B (UVB) energy converts the precursor (Skin’s cholesterol) to vitamin D3.
In contrast, most supplements are manufactured by exposing a plant sterol/ ergosterol (a bio compound that is extracted from Fungi) to UV irradiation, thus producing vitamin D2. Whereas, Vitamin D3 is manufactured by the irradiation of 7-dehydrocholesterol from lanolin (Wax extracted from sheep’s wool). Because their function is almost identical, D2 and D3 are lumped together under the name vitamin D — but neither will function until the body works its magic.

HOW DOES THE BODY PROCESS VITAMIN D?
After vitamin D is absorbed through the skin or acquired from food or supplements, it gets stored in the body’s fat cells. Here it remains inactive until it’s needed. Through a process called hydroxylation, the liver and kidneys turn the stored vitamin D into the active form the body needs (called calcitriol).
Detailing it- the first stop is in the liver, where vitamin D picks up extra oxygen and hydrogen molecules to become 25-hydroxyvitamin D, or 25(OH)D. Now, this is the chemical that doctors/laboratory techies usually measure to diagnose vitamin D deficiencies. But although 25(OH)D is used for diagnosis, it can't function until it travels to the kidney. There it acquires a final pair of oxygen and hydrogen molecules to become 1,25 dihydroxyvitamin D; scientists know this active form of the vitamin as 1,25(OH)2D or calcitriol, but for laymen, the name vitamin D is accurate enough.
(This simple is what I could decode from the scientific papers that I referred to. )
Without enough vitamin D, the body can only absorb 10% to 15% of dietary calcium, but 30% to 40% absorption is the rule when vitamin reserves are normal. Low levels of vitamin D lead to low bone calcium stores, increasing the risk of fractures and bone-related issues.
Researchers have accumulated evidence that vitamin D worked more than protecting our bones. In fact, many of the body's tissues contain vitamin D receptors, proteins that bind to vitamin D. In the intestines, the receptors capture vitamin D, enabling efficient calcium absorption. But similar receptors are also present in many other organs, from the prostate to the heart, blood vessels, muscles, and endocrine glands. And work in progress suggests that good things happen when vitamin D binds to these receptors.
Another interesting and important news is that Vit D turns to also play an important role in our respiratory health through its effects on lung development and structure, respiratory muscle strength, inflammation and immune response to respiratory pathogens.
Pic Source: Google 
THE MORE VITAMIN D YOU TAKE, THE BETTER? ABSOLUTELY NOT.
That’s a misconception. Vitamin D is stored in fat. So, if you’re a small person and getting large doses, you have less available storage, which means vitamin D goes into your blood and you may absorb too much calcium, creating a toxic situation. And it’s still unclear how long you have until you exceed the upper limits of vitamin D intake before it becomes dangerous.

SHOULD EVERYONE GET THEIR VITAMIN D LEVELS CHECKED? GENERALLY, NO.
Most people should be fine. Testing is important only for certain populations: for people who have deficiency symptoms; for patients with a gastrointestinal disorder or osteoporosis; those on anti-convulsant medications; and those who are immobilized and not outside and active. If you’re over 70, it’s recommended getting your levels checked at least one time.
People whose cultural or religious beliefs require them to be fully clothed, especially if they’re living in northern climates, and whose dietary habits include little or no Vit D rich foods may also be vitamin D-deficient and should be tested.

IS IT BEST TO GET YOUR VITAMIN D FROM THE SUN? DEFINITELY YES!
Expose Your Skin around Midday which is the best time to get sunlight. Since at noon, the sun is at its highest point, and its UVB rays are most intense. That means you need less time in the sun to make sufficient vitamin D than in the early morning sun.
Now, darker-skinned people have more melanin, a compound that protects against skin damage by reducing the amount of UVB light absorbed. Darker-skinned people need more time in sunlight to make vitamin D.
People who live farther away from the Equator like near Polar Regions need more time in the sun and during winter months as they cannot make vitamin D from sunlight, so they are the ones who need to get it from foods and/or supplements if needed.

Wearing light clothes and with exposure for 7–10 minutes during the mid day would suffice.

One of the biggest challenges faced in dermatology and in the world of skin cancer prevention has been a lot of misinformation about getting exposed to sun, which is absolutely false. One needs to get a certain amount of sun exposure every day in order to produce enough vitamin D to be healthy.
Both your skin and your bones will thank you.
Pic Source: Google 
On a simple note don’t panic and take it heavily. Just get a "healthy" tan and your body will make all the vitamin D it needs. For us (Indians) Desk jobs and sunscreen have changed all that, just as research is underlining the importance of vitamin D and suggesting its possible role in preventing many health problems. That makes vitamin D a dilemma of modern life that has a modern solution: eating and drinking fortified foods, along with (judicious) doses of vitamin D supplements.
All in all, it’s important to remember that while vitamin D can help ward off respiratory infections in some people, always make sure to discuss taking supplements with your healthcare provider—because supplements may not always be safe for everyone.
(Another avenue (note: another avenue) to get vitamin D is by taking supplements. These come in both pill and liquid form. They are generally recommended for people with fat absorption issues, lactose intolerance, vegans, mushrooms and milk allergies, as well as for people with very darker skin tones or with certain medical conditions that prevent them from going outdoors.)
In case one goes for supplements, always look for ones that offer the daily recommended allowance (RDA) you need for your age bracket: For most healthy people, it’s 600 IU per day, but for people over age 70 who need a little more—it’s about 800 IU. That’s because, as people age (women after menopause, in particular), they less efficiently synthesize vitamin D and absorb calcium. Babies should be getting smaller amounts in their first year of life, between 200 and 400 IU.


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