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Vitamin D Deficiency

If (photo)synthesis of vitamin D is not your thing...

Plants are fueled by it. Algae can get nourishment from it. We, inept humans can only sulk in awe as other living things harness the power of the sun. But while we fantasize about harnessing our super brain powers to genetically engineer photosynthesis in humans (think: Marvel Comics’ Cyclops version 2), consider this: our skin can produce vitamin D from sunlight. 

Whoop-dee-do. We can make vitamin D

Comparatively an evolution consolation prize, we can harness the power of the sun to make vitamin D from cholesterol, something that we have plenty of (or plenty of access to). The ‘photosynthesis’ of vitamin D begins in the skin with activation of a cholesterol molecule to previtamin D3 by ultraviolet (UV) light from the sun. Heating and chemical conversion of the precursor vitamin molecule continues in the skin. The process then moves to the liver for further chemical modification, then on to the kidneys for a final tweak. And voila! We generate vitamin D (or calciferol) for our intestinal calcium/phosphate absorbing needs. 

How much sun exposure to get that vitamin D factory going?

The short answer: It’s variable and don’t count on it.

Most of us can meet at least some of our vitamin D needs through exposure to sunlight. Potentially, 50% to 90% of our vitamin D needs can be synthesized via sunlight. Variables such as cloud cover, smog, skin melanin content, the season, time of day, length of day, and sunscreen can affect the efficiency of this photochemical process. These factors make universal guidelines on how much sun exposure is required for sufficient vitamin D exposure difficult. Nevertheless, some experts suggest that approximately 5 to 30 minutes of sun exposure, either daily or at least twice a week, to the face, arms, hands, and legs should lead to sufficient vitamin D synthesis. 

But before we wipe off the sunscreen, let’s not forget the prickly fact that to jumpstart the process of vitamin D synthesis, we’d have to bake our skin with ultraviolet radiation- the same radiation that’s classified as a carcinogen. Despite our desire to harness benefits from sun exposure, it makes sense to limit our exposure to UV radiation in order to prevent skin cancer.

So what’s a Sun-shunning person to do?

Work with your doctor to determine if you are vitamin D deficient. Your doctor can help you reach, and then maintain, an adequate level of vitamin D in the body. Commonly ingested sources of vitamin D are:

Food sources

Very few foods naturally contain vitamin D. Except for pescetarians or connoisseurs of fatty fish livers, it may be difficult to get enough vitamin D from diet alone. This is an especially difficult task for vegans or people who are lactose-intolerant. Ultimately, many folks may have to take supplements to meet their daily needs.


Vitamin D comes in two forms: D2 and D3. Vitamin D3 is more easily absorbed and has been shown to be better in achieving optimal vitamin D levels in the blood. The need to supplement and the amount of vitamin D supplementation should be determined by your doctor. Generally speaking:

  • Adults younger than 65 years of age who do not have year-round effective sun exposure should take 600 to 800 international units (IU) of vitamin D3 daily

  • Adults 65 years of age and older should take 800 to 1000 IU of vitamin D3 daily


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