Vitamin D – everything you need to know

Underestimated, but extremely necessary vitamin

Did you know that it took more than 200 years to prove the vital role of the fat-soluble vitamin D, part of one of the most important groups of micronutrients for the human body? The first suggestion of this was the discovery that the consumption of cod liver oil had an extremely beneficial effect on the health condition rickets.

Over the time, it became clear that vitamin D was discovered in 1782 and isolated only in the early 1920s, and today, at the beginning of the 21st century, not only its role against rickets conditions, but also its particularly beneficial effects to the immune and nervous systems.

Vitamin D deficiency and low levels in the body lead to the development of more than 50 pathological conditions, including cardiovascular, neoplastic diseases (that cause tutor growth) and diabetes.

№1 Deficit in the modern western world

Vitamin D deficiency has been found to be most prevalent in modern countries outside the equatorial and tropical zones. This is particularly true for countries in North America, Europe, Asia, and southern South America. Most affected are populations in the northern US, Scandinavian countries, the UK, and Russia.

More serious statistics on vitamin D deficiency have been kept since 1988. The recommended serum vitamin D concentration of 75 nmol/L is used as a criterion. In 1988 55% of the population suffered from deficiency, the percentage in 2004 was 77% and nowadays it is 79%. Statistics show that nearly 29% of the US population has vitamin D levels below 50nmol/L. Of course, these numbers are relative, because the percentages change based on the time of the year.

Despite the role of geography, there are a lot of places in the tropical belt whose population suffers from vitamin D deficiency. For example, in one of the southernmost Iranian cities, nearly 50% of the population suffers from low levels of the vitamin. While in Iran cultural characteristics and clothing are influential, there is no similar excuse for the people of Florida, where 38-40% of the population score levels lower than 50nmol/L.

Certain population groups are at higher risk of deficiency. These are most commonly individuals in various medical conditions, pregnant women, and those belonging to races with darker skin.

Although a large proportion of the population is not deficient, it is interesting to note that vitamin D levels are not in the optimal range for maintaining good health.

What is vitamin D

Vitamin D belongs to the group of fat-soluble vitamins and is extremely rare in nature. In the form of an active vitamin, it exists mainly in animal products, including fish, liver oil, liver, animal fats, cow’s butter, and egg yolk.

The fat-soluble vitamin exists in several varieties (D1, D2, D3, D4 and D5), but with medicinal value, are only vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol, which when activated in the body is converted into a powerful steroid hormone), which are similar in structure, properties, and action on the body.

They are synthesized from cholesterol, and its main source for humans is the 7-dehydrocholesterol of the skin, from which it is obtained when irradiated with ultraviolet rays.

They are transported into the blood, bound to plasma globulins, deposited in the kidneys and liver, and are involved in the metabolism of phosphorus and calcium. Without vitamin D, parathyroid hormone, which is the main hormone synthesized and secreted by the parathyroid glands, does not exert its full action.

What do you need to know about vitamin D?

What is unique about the vitamins is that they are absolutely necessary in small amounts to maintain the normal functioning and health of humans and animals, as well as their proper development.

Their deficiency in the diet disturbs the proper course of almost all physiological processes. Vitamin D is no exception in this respect, as there is already sufficient scientific evidence to prove its preventive and curative functions.

Proven benefits for humans

  • Lowering the risk of falls and bone fractures in the elderly. A stronger effect is noted when combined with calcium;
  • Improving muscle and neural functionality in the elderly;
  • Reduced risk of cardiovascular disease or complications of such diseases;
  • A direct relationship between vitamin D levels and high blood pressure has been demonstrated. Higher
  • concentrations of the vitamin D lead to lower blood pressure;
  • Directly affects the regulation of parathyroid hormone secretion. Used as a reference medication;
  • Dramatically lower (50%) the risk of colon cancer;Reduces the occurrence of asthmatic attacks in young individuals;
  • High vitamin D levels in children are associated with greater height growth. No similar effect is noted in adults;
  • Improve insulin secretion in individuals with type II diabetes or individuals at risk. The effect is directly correlated with the protective properties at the level of the pancreas;
  • Improvement of insulin sensitivity as a result of improved insulin secretion from the pancreas;
  • Reduction of inflammation in systemic lupus erythematosus (autoimmune disease);
  • Reduction of symptoms in tuberculosis;
  • Slight decrease in the pro-inflammatory cytokine tumor necrosis factor alpha with long-term intake;
  • Slightly lowers the blood triglyceride levels after long-term use;
  • Increase in the low testosterone by 30% in men after one year of use. Low testosterone may be result of vitamin deficiency;
  • High serum vitamin D levels improve calcium metabolism and absorption;
  • Lowers the risk of developing multiple sclerosis significantly, as well as reducing some of the symptoms of one that has already occurred;
  • Vitamin D supplementation has been associated with a reduced risk of breast cancer, pancreatic cancer, prostate cancer, and ovarian cancer;
  • Vitamin D deficiency is associated with low mood and depression. There is a direct link between vitamin D supplementation and symptom reduction in depression;
  • Optimal serum vitamin D levels positively impact seminal fluid quality.

Potential benefits in humans

  • There is strong suggestion that low vitamin D levels are associated with fat accumulation. Almost all overweight individuals are deficient in the vitamin. It is possible that optimal levels of vitamin D may help to maintain a leaner shape and healthy percent of body fat.
  • A direct link has been found between high serum vitamin D levels in the elderly and lower mortality. It is possible that mortality is lowered due to improved general health or reduction in falls.
  • Not enough data about lowering the risk of contracting influenza.
  • Controversial results on the increase in physical strength after vitamin D use. It may increase strength and explosiveness as well as improving recovery after exercise.
  • Potential benefits in lowering symptoms of arthralgia (joint pain).
  • May lower the risk of developing type I diabetes.
  • Low vitamin D levels are associated with sleep problems, but there is insufficient evidence at this stage that vitamin D supplementation can improve sleep quality.
  • Potential benefits in the treatment of atherosclerosis.
  • Potential benefits in regulating aromatization, using calcium metabolism.
  • Hypothetical protective effect on the lungs in smokers.

How much vitamin D should we take?

The recommended daily intake of vitamin D for adult men and women ranges between 400 IU and 800 IU, but most studies find this to be an extremely small and ineffective dose.

The recommended safe maximum dose in the U.S. and Canada is 4,000 IU, although clinical tests have found that a daily dose of 10,000 IU is perfectly safe, and an even higher dose may be taken in some health conditions.

Based on practice, the following recommended doses can be derived:

  • For adult men and women – a minimum effective dose of 2000-3000 IU daily.
  • For athletes – 3000-5000 IU daily.
  • For patients with osteoporosis and rickets – 5000-10 000 IU.
  • For babies and children – 500-1000 IU daily.

In some cases, high doses of vitamin D can lead to intoxication. A daily intake of more than 20 000 IU is not recommended. However, if taking the vitamin once a week, then the toxic dose exceeds 300,000 IU.

Getting vitamin D from the food and the sun

Food sources that contain significant amounts of vitamin D are relatively few. Two categories of food are major sources:

  • Cod liver oil – the concentration depends on the sources of the oil and the method of processing. Note that 1 ml of oil provides 2.54-2.78 mcg of vitamin D.
  • Dairy products – milk is considered a major source of vitamin D, with concentrations again dependent on the quality of the milk and processing. For information, 230 ml of pasteurized milk provides 100 IU of vitamin D, which is simply not enough.

The main natural source of vitamin D is the sun. UV rays meet the skin and the stored 7-dehydrocholesterol is converted to cholecalciferol (D-3).

However, in some cases there are factors that reduce the synthesis of vitamin D by sunlight:

  • At latitudes farther from the equator, vitamin D synthesis is lower because of weak UV rays.
  • Weather and season, clouds and darkness reduce the sun’s rays.
  • Combination of latitude and season. At some latitudes in the northern hemisphere, between October and March, no vitamin D can be synthesized.
  • In areas with a thinned ozone layer.
  • In people with dark skin.
  • The use of sunscreens, which directly affect vitamin D levels negatively.

Supplementation with vitamin D: forms and method of taking

There are two main forms of vitamin D found on the market. One is vitamin D-2 (ergocalciferol), which is derived from plants, and the other is D-3 (cholecalciferol), which is derived from animals and fish. It is vitamin D-3 that is found in one of the best quality sources of the vitamin, which is cod liver oil.

Vitamin D-3 is better absorbed and increases serum vitamin D levels in the body more. There is one study that claims that D-2 is just as effective as D-3, but most reputable studies show just the opposite. Therefore, the science recommendation is that when choosing vitamin D as a dietary supplement, it should be in the form of vitamin D-3 (cholecalciferol).

Vitamin D is best absorbed with a small amount of fat, and the type of fat does not matter. Some authors recommend combining with fish oil for better absorption. Vitamin D has been found to be better absorbed with 10 – 20 grams of fat, compared to no fat intake, intake on an empty stomach, or with food containing more than 35 grams of fat.

What does an overdose of vitamin D leads to?

As I mentioned, vitamin D is formed in the skin under the influence of the sun’s ultraviolet rays, but the good news is that there is no risk of toxicity with prolonged sun exposure.

On the other hand, the physiological action of the fat-soluble vitamin is related to the regulation and metabolism of calcium and phosphorus in the body, i.e., vitamin D ensures the deposition of both calcium and phosphate ions.

An excess would lead to abnormally high levels of these ions in the blood, resulting in a real danger of bone, kidney, and soft tissue damage. This means only one thing – the additional intake of the vitamin must necessarily be consulted with health practitioner.

The main symptoms of toxicity due to vitamin D overdose are:

  • Fatigue and irritability.
  • Headache, unclear speech.
  • Dehydration with constipation.
  • Decreased appetite and sharp reduction in body weight.
  • Muscle weakness.
  • High blood calcium levels (hypercalcemia)

The question is how to protect ourselves from vitamin overdose? And the answer is simple – by monitoring the blood status of the fat-soluble vitamin. In addition, a blood test would give us confidence that the vitamin D level is within normal range.

Experts recommend periodic testing (every six months) to protect you from possible toxicity caused by additional supplementation.

Treatment in these cases usually involves rehydration, stopping the intake of any type of supplement that includes in its content vitamin D, and limiting calcium intake.

Hypersensitivity to vitamin D

In some cases, some people are found to be hypersensitive to supplemental vitamin D intake. It is usually seen in patients suffering from hyperparathyroidism (this causes the levels of calcium in your blood to rise, a condition known as hypercalcemia), sarcoidosis (disease involving abnormal collections of inflammatory cells that form lumps known as granulomata), and certain types of neoplastic diseases. But on the other hand, what is the cause of low levels of the fat-soluble vitamin?

The simplest and yet most logical explanation is the lack of direct sunlight. Considering the peculiarities of the climate in the latitude people are located, we usually wear more clothes than necessary.

In addition, people who live in big cities suffer from vitamin D deficiency, not only because of the daily morning fog that absorbs UV rays, but also because of the high-rise buildings.

Also, when we decide to go outdoors, we usually choose a high factor sunscreen lotion, which certainly provides us with good prevention against sunburn, skin aging and cancer, but also against the positive effect of vitamin D.

Diseases associated with low levels of vitamin D

Optimal levels of this vitamin in the body significantly improve the function of the immune, nervous and bone systems, and deficiency is associated with a number of diseases, the most common are:

  • Acne, various allergic conditions.
  • Autism, Alzheimer’s disease, Parkinson’s disease, dementia, depression.
  • Kidney failure, arthritis.
  • Breast, colon, and ovarian cancer.
  • Chronic fatigue, colds, and various bacterial and viral infections.
  • Formation of dental cavities and poorly coordinated teeth, development of periodontitis.
  • Gluten intolerance.
  • Osteoporosis, osteomalacia, muscle weakness, pain, rheumatoid arthritis, rickets, frequent sports injuries.
  • Chronic obstructive pulmonary disease, tuberculosis.
  • Hypertension
  • Diabetes (type 1 and 2), obesity.
  • Psoriasis

With what to combine vitamin D

Vitamin D can be combined with other fat – soluble vitamins, such as vitamin K-2. The two vitamins have similar and complementary properties with respect to cardiovascular function, insulin sensitivity and the motor system.

Vitamin D is combined with calcium because it plays an important role in its metabolism and dramatically improves its absorption.

Combining vitamin D with fish oil is recommended as a quality source of beneficial fats.

For general health and combining various health effects, vitamin D is successfully combined with zinc and magnesium


We know that vitamins are not building blocks, much less a source of energy, but our body needs them.

That’s why vitamin D, as part of a complex nutrient system, needs other supporting substances to function properly. These are calcium, magnesium, zinc, boron and vitamins A and K2. Without them, the function of the fat-soluble vitamin will not be effective.

Of course, the best way to get these nutrients is to consume organic plant foods – enough fruits and vegetables, whole grains, seeds and nuts, and organic animal products – liver, milk, butter, cheese, cottage cheese, egg yolks. The choice is yours.


  1. Brock K, et al Low vitamin D status is associated with physical inactivity, obesity and low vitamin D intake in a large US sample of healthy middle-aged men and women. J Steroid Biochem Mol Biol. (2010)
  2. Levis S, et al Vitamin d deficiency and seasonal variation in an adult South Florida population. J Clin Endocrinol Metab. (2005)
  3. Heaney RP, et al Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr. (2003)
  4. Vieth R Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr. (1999)
  5. Houghton LA, Vieth R The case against ergocalciferol (vitamin D2) as a vitamin supplement. Am J Clin Nutr. (2006)
  6. Dawson-Hughes B1, et al Meal conditions affect the absorption of supplemental vitamin D3 but not the plasma 25-hydroxyvitamin D response to supplementation. J Bone Miner Res. (2013)
  7. Vieth R Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr. (1999)

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