Unexpected Downfall in Level of Vitamin D: Is Something Apprehensive

Last few years, I am astonished to see the posters which are guiding us to go for regular checkup of vitamin D? And in these results, I didn’t find anyone is having the Vitamin D in optimal condition. This is could only due to 2 reasons, one is the sudden decreased in the level of vitamin for which no satisfied explanation is appeared or it may be scripted.

Vitamin D has been in controversies due to its dual nature, i.e. vitamin or hormone, as it doesn't fit in the definition of the vitamin. This is synthesized by the body itself, while for a vitamin, one has to take outside. However, a very good article is available on various biochemical and metabolic aspect of vitamin D. The aim of present text is to put the facts in an analytical way so that people can understand what should they do.

Basic Biology of Vitamin D

Facts shall examine under following headings

Optimal level of Vitamin D

Requirement of vitamin D varies mainly with age, along with pregnancy and lactation. As per international standards, middle-aged group (1-70 years), its 15 microgram, while its raise to 20 micrograms to persons older than 70 years. 

Most people in the world meet at least some of their vitamin D needs through exposure to sunlight [1]. Type B UV (UVB) radiation with a wavelength of approximately 290–320 nanometers penetrates uncovered skin and converts cutaneous 7-dehydrocholesterol to previtamin D₃, which in turn becomes vitamin D₃. Season, time of day, length of day, cloud cover, smog, skin melanin content, and sunscreen are among the factors that affect UV radiation exposure and vitamin D synthesis. Older people and people with dark skin are less able to produce vitamin D from sunlight [1]. UVB radiation does not penetrate glass, so exposure to sunshine indoors through a window does not produce vitamin D [2].

Research (Glerup et. al 2001) showed that even if you have enough vitamin D intake, if you are not exposed to sunlight will not going to maintain the required level of Vitamin D3, a pro-metabolic form, which body use as per need. Their results suggested that the daily oral intake of vitamin D in sunlight‐deprived individuals should exceed 15 mcg, most probably it should be 25 mcg/day to secure a normal level of 25‐hydroxyvitamin D [3].

During the initial exposure to sunlight, provitamin D3 is efficiently converted to previtamin D3. However, because previtamin D3 is photolabile, continued exposure to sunlight causes the isomerization of previtamin D3, principally to lumisterol [4]. Therefore, exposing your body for hours near seashore is not going to give you due benefits, instead of intermittent exposure, may do so. To maintain healthy blood levels, aim to get 10–30 minutes of midday sunlight, several times per week. People with darker skin may need a little more than this. Your exposure time should depend on how sensitive your skin is to sunlight. Just make sure not to burn [5]

 External Sources and its Amount

There are not much natural sources of vitamin D in daily diet of Indian, food, if you are vegetarian and not taking 2 American Cup (250 ml) of milk and one cup of curd, and cereals as per your need. This will fulfil your need of 15 micrograms (requirement from age of 1 to 70 years). However, the main source of the vitamin is cod liver oil and other fish meat, especially Salmonidae family. So if you are non-vegetarian need not to worry and have some change in diet habit, add fish in the diet once in a week. An average data is given in the graph. Nevertheless, no amount of suppliment can replace the sun bath. 

 

Now consider the above graph, one can easily see understand that 2 cups of milk and one serving size of cereals can’t meet the requirement of vitamin D until and unless we feed on fishes or mushrooms. However, their absorption is also a difficult issue to deal with and therefore their bioavailability. Thus the only option is sunbathing, as any artificial source will not going to help you.

Absorption of Vitamin D in Gut

The absorption of vitamin D in intestinal absorption is not passive only but involves, at least partly, some cholesterol transporters [6]. Researchers have shown that vitamin D is absorbed in the median intestine. Significant competitive interactions for uptake were then elucidated among vitamin D, E and K, supporting the hypothesis of common absorption pathways. Vitamin A also significantly decreased the uptake of the other FSVs but, conversely, its uptake was not impaired by vitamins D and K and even promoted by vitamin E. These results should be taken into account, especially for supplement formulation, to optimize Fat Soluble Vitamin absorption [7].

Looking at the changed life style and keeping in mind our official dress codes, which is useless, especially in Indian perspective, (anyway we can’t change it, as of now), we have to assure, that at least weekend can be spare for the 2-3 hrs for sun bathing, intermittently which will enough amount for the week. The half-life of vitamin D is 15 days.

So even if you take vitamin D in form of pills, primarily it will not absorbed, and even if it absorbed if will not metabolic active form, which body can utilized. Body store it in previtamin form, which converts as requirement. The fact is simply evidenced from research of Glerup et. al (2001), which showed in their experiment that even after taking sufficient dose, the blood level was up to optimal level.