Vitamin-D the metabolic marker


First things first: Vitamin-D is  … not a Vitamin! It is not a true vitamin because the human body has the capacity to
synthesize its own cholecalciferol (D3), endogenously through ultraviolet exposure of the skin (UV-B radiation). It is more accurate to view it as a steroid hormone. 
Vitamin-D can also be received from diet, but with a very small contribution to the total. It is estimated that around 90% of the body’s VitD comes from sun exposure, leaving merely a 10% to dietary sources.

So we need to get more sun right? Yes! and as simple as it may sound so many people are deficient in Vitamin-D.

Today we will discuss, why I like to think Vitamin-D as a first indicator of our metabolic health.

Some history first

The first studies on Vitamin D involved children’s rickets condition and resulted in the undisputed acknowledgment of D’s contribution to bone health. It was around late 50s that the food industry started fortifying certain foods with VitD (especially those consumed by children eg infant formulas, cereals and dairy products).  Unfortunately, this limited understanding of VitD continued through the decades. Even today, many doctors only see Vit D as a bone supporter and thus fail to link a potential D deficiency of their patients with other underlying conditions. Of we should highlight that the need of Vitamin-D for strong bones is crucial but the requirement for Vitamin-D goes far beyond that.

The benefits of Vitamin-D

What we know today is that there a wide spectrum of potential Vitamin-D health benefits. Research so far suggests that vitamin-D  plays a role in many other areas. This is also supported by the fact that literally every cell in our body has Vitamin-D receptors.

Vitamin-D helps with

  • strong bones and absorption of calcium into the bones. Calcium and vitamin D work together to protect your bones.
  • supporting the immune  system (decreased risk for auto-immune diseases like MS and psoriasis)
  • regulating the mood and fighting depression
  • fighting inflammation and muscle repair
  • influencing the expression of genes involved in cancer development
  • supporting the brain, and nervous system health (prevention of Alzheimer’s and other forms of dementia)
  • decreasing the chance of developing heart disease (regulation of hyper-tension)
  • protecting  against the influenza virus  (Studies are now being conducted for VitD efficacy in avoiding COVID-19 infections)
  • supporting lung function 
  • supporting people with asthma
  • supporting weight loss (especially beneficial for visceral fat) 
  • decreasing risk for preeclampsia or C-section in pregnant women

Vitamin-D as a metabolic marker

Vitamin-D can be a good marker of metabolic health, since there are many steps required to activate it and make use of it.

  • Cholesterol : Cholesterol is a precursor to creation of hormones. In fact you sythesize every single sex hormone from cholestore and Vitamin-D is in the same category. We need cholesterol in our skins cells to make vitamin D from sunlight. The vitamin D is later transformed again in the liver and kidneys, but cholesterol is needed for the first step. You should not be afraid of cholesterol!
  • Insulin : High levels of insulin block the very first enzyme that converts cholesterol into Vitamin-D. That is why obesity and diabetis is linked to low levels of Vitamin-D. High levels of insulin cause insulin resistance which is at the root of many modern decease.
  • Healthy GI track : Diatery intake of Vitamin-D is absorbed from the small intestine. People with conditions such as inflammatory bowel disease, may have trouble absorbing vitamin-D.
  • Healthy Liver and Bile : Vitamin-D requires a healthy liver and bile to go through a process of Hydroxylation. If you have a fatty liver or you don’t produce enough bile this process will be impaired.
  • Fat intake : Vitamin-D also requires diatery fat, similar to the other fat-soluble vitamins. If you follow a low-fat diet your absorption of vitamin-D will be impacted.
  • Healthy Kidneys : You also need healthy kidneys as a last to produce 25(OH)2D which is the active form your cells use.


You now should have an idea how many steps we need to go through until our cells start using Vitamin-D (and not only). 


  • Even if you are getting enough sun exposure, you might have low Vitamin-D if you are not metabolically healthy.
  • Vitamin-D levels can give us a good indication of our metabolic health. Other indicators are high blood glucose, low levels of HDL cholesterol, high levels of triglycerides in the blood, and increased BMI (weight).

The D-pandemic

As  awareness is being created and more people have their D levels tested, the collected statistics reveal extremely high
percentages of deficiency, even in countries with high exposure to sunlight. A recent reseach in Greece based on 60K samples found that the average Vitamin-D levels were ~20 ng/ml of vit D in vast majority, when the “official” normal range is from 30 to 50. That is a big issue!

When it comes to sun exposure, it is important to get plenty of sun as often as possible! But be aware of :

  • Sunscreens : This is huge! A sunscreen with a sun protection factor (SPF) of 30 can reduce the body’s ability to synthesize the vitamin by 95%. Avoid sunscreens! Even if you are sensitive to sun you can build your tolerance, by exposing yourself to the sun for a few minutes at a time.
  • Location: Geographical location, specifically latitude has a major influence on vitamin-D levels. The further we are from the equator, the lower the strength of the sun and the lower the potential to produce vitamin-D. People that live in latitudes > 37° are at higher risk for deficiency 
  • Season: In the summer, the sun is higher in the sky, which means less UV radiation is filtered by the atmosphere, and also the daytimes are longer. However, staying indoors will not produce any Vitamin-D since the UVB spectrum does not penetrate the glass. Direct exposure of the skin to sun is therefore required 
  • Skin color: People with darker skin typically have lower levels of vitamin-D than lighter-skinned individuals. African Americans have, on average, about half as much vitamin-D in their blood compared with white Americans. An interesting theory is one claiming that Vitamin-D was the main evolution driver for losing the pigment gene i.e as people started moving to northern areas, the skin color lightened to allow the maintenance of Vitamin-D synthesis.

So much sun do we need

The body has a large capacity to make vitamin D with minimum sun exposure. Studies claim it is enough if a light-skinned person exposes (during Spring/Summer periods).

  • Expose as much skin as possible (or minimum 20% of our body)
  • For around 20 minutes
  • Minimum of 2-3 times a week
  • Between 10:00 to 15:00 (max effect within 11:00 to 13:00) 



  • Get as much of sun exposure as possible on a daily basis and avoid suncreams.
  • Listen to your body by exposing yourself to the sun without getting burned.
Getting some sun even in winter!

Vitamin-D diatery sources

There are 2 sources of importance

  • Animal-derived VitD  is D3 (cholecalciferol) found in fatty fish, cod liver oil, egg yolks, butter and liver.
  • Plant-derived VitD is D2 (ergocalciferol) found in mushrooms (especially those exposed in high UV radiation) and fortified products.

Some studies point to the two being equal while other to D3 being superior. The points of interest in such studies are usually: 1) the efficacy in raising the Vit D level in blood circulation, 2) the ability to sustain this level for longer periods. And while the first point is still disputed due to controversial findings, the second clearly puts D3 to the winning podium.

Facts and Tips

  • Sun is alwas better : Vitamin D from sun exposure lasts 3 times longer compared to dietary D, or the one taken via supplements.
  • Prefer high quality foods : Farm fish has far less D3 that wild caught fish.
  • Include mushrooms : Vitamin-D in mushrooms can increase significantly by drying them under the sunlight for two days, six hours per day.
  • Vitamin D is fat-soluble :  If supplementing take with a meal that contains moderate amount of fats. Absorption can increase as much as 30%
  • Probiotics : A probiotic called LRC (Lactobacillus Reuteri DSM 17938) was proven to enhance Vitamin-D bio-availability in the body by 25%
  • Get sun indoors: There are UVB lamps available in the market, mainly used to radiate in-door kept pets (reptiles) so that they produce more Vitamin D. Some people use them also for their own vitamin synthesis.
  • There are no side-effects : Vitamin D toxicity is extremely rare.
  • Plant D3 : Lichen –although a plant- was found to also produce D3. It is the first Vitamin D3 source approved by the Vegan and Vegetarian society.


Supplementing in winter when you can’t get enough sun is fine. Since sun exposure during winter is not always easy, and the effectiveness of synthesis is in general compromised due to the sunrays’ angle supplementing with Vitamin-D is probably a good strategy. Adults can go up to 10000IU.

Key Takeaways

A special thanks to Christina for the great research and support on writing the article! If would like to also contribute just drop us a message!

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