How much vitamin D do you need and what is the best way to prevent a deficiency?

Until the industrial revolution, vitamin D deficiency was a rare condition. 

But shortly before the beginning of the 21st century, scientists estimated that over 90% of children living in cities suffered from severe vitamin D deficiency and its associated symptoms, such as rickets. [1].

Only then was it discovered that vitamin D deficiency was due to insufficient exposure to direct sunlight and led to debilitating complications such as rickets.

However, nowadays people spend more time at home than ever before.

This sedentary lifestyle leads to an increased incidence of vitamin D deficiency, and as a result, scientists report that about 50% of the world's population is currently deficient. [2]. 

Many scientists even compare vitamin D deficiency to a pandemic, as it affects people of all ages, genders, races, and regions. [3], [4]. 

It's also likely that your vitamin D levels are insufficient, especially during the winter months unless you spend time in the sun daily.

Not to mention that there are only a few good food sources as an alternative, and the vitamin D content in them varies widely.

This is why experts around the world recommend taking vitamin D supplements.

In this article, you will find everything you need to know about the best way to get enough vitamin D and how to correct your deficiency quickly, safely, and effectively.

What is vitamin D?

Vitamin D, also known as the sunshine vitamin, is one of the first hormones produced by living organisms. According to scientists, protozoa began synthesizing it 750 million years ago.

It is often called a prohormone because the human body can produce it and food is not its only source, unlike most other vitamins.

Vitamin D is actually a combination of several fat-soluble vitamins, the most significant of which are D2 and D3.

Vitamin D3 is formed in your skin when exposed to direct sunlight, which breaks down one of the precursors of cholesterol. In addition, many animals, as well as algae, can also produce vitamin D.3.

On the other hand, vitamin D2 is only produced in plants. Therefore, depending on whether a food source is of plant or animal origin, it may contain either D2, or D3.

What are the causes of vitamin D deficiency?

Currently, the increasingly sedentary lifestyle of modern people is the main cause of low levels and lack of vitamin D.

Among the aspects that contribute to the less frequent stay indoors in recent years are also the COVID-19 pandemic and the increased use of modern technologies.

In addition, the season, as well as the level of air pollution, play a significant role. Vitamin D deficiency is most common during the winter and spring seasons, especially in cities with highly polluted air like Sofia.

All factors that can increase the risk of vitamin D deficiency include:

• time spent indoors
• geographical location and season
• air pollution
• clothing
• skin color
• aging
• excessive use of sunscreen products
• medications (corticosteroids, laxatives, orlistat, etc.)

The best way to find out whether you have a deficiency or not is to get a vitamin D test done in a laboratory. 

However, direct measurement of the vitamin in the blood is not a reliable marker. Instead, the biomarker for vitamin D status is called 25-hydroxyvitamin D.

According to the International Endocrinology Society guideline, 25-hydroxy vitamin D levels should be above 30 ng/ml (75 nmol/l) to minimize the possible risks of vitamin D deficiency. [5].

Furthermore, studies show that levels below 20 ng/ml (50 nmol/l) suggest deficiency and a high risk of sequelae. [6]. The most common consequences of deficiency are an increased risk of bone fractures and the so-called bone disease osteomalacia.

Levels below 12 ng/ml (30 nmol/l) are considered dangerous, as such a severe deficiency is a risk factor for various infectious diseases, cancer, and premature death.

What are the consequences of a lack of vitamin D?

Almost every cell in the human body has a receptor for vitamin D [7]. Therefore, most tissues and organs need certain levels to function properly.

Most importantly, the vitamin is necessary for intestinal absorption and maintaining adequate levels of calcium in the blood.

This is why vitamin D deficiency leads to insufficient serum calcium levels and bone problems. In children, low calcium levels lead to bone development problems known as rickets.

In adults, deficiency can lead to osteoporosis and osteomalacia. [8], [9]. Osteoporosis increases the risk of bone fractures, while osteomalacia means „soft bones“ and can cause bone pain and disability.

Additionally, studies show that low vitamin D levels may be associated with an increased risk of:

• heart disease and mortality [10], [11]
• autoimmune diseases such as type 1 diabetes [12] and multiple sclerosis [13]
• respiratory infections [14]
• malignant diseases such as colon cancer [15], the breast [16], pancreas [17] and the ovaries [18]
• depression [19]
• Parkinson's [20]
• insulin resistance and type 2 diabetes [21], [22]
• ovarian dysfunction and reduced fertility [23]
• problems getting pregnant [24]

Does vitamin D deficiency lead to obesity?

Most evidence suggests that patients with lower vitamin D levels lose less fat during weight loss interventions. Therefore, deficiency may be a risk factor for overweight or obesity.

For example, a study in 218 women showed that those who remained deficient (<32 ng/ml) after supplementation lost less body fat and weight compared to those who became deficient. [25].

Supplementing with vitamin D does not appear to promote weight loss, but correcting a vitamin D deficiency may help you control your body weight.

Another study in 77 women also did not report significant weight loss with vitamin D supplementation, but supplemental intake did lead to a greater reduction in body fat mass. [26].

Additionally, supplemental vitamin D may also enhance the cardiovascular benefits of a weight loss program. [27].

Several studies have reported improved physical performance after correcting vitamin D deficiency, which may further enhance your fat-burning efforts. [28], [29].

Which foods have the highest vitamin D content?

Unfortunately, there are only a few foods that are naturally good sources of vitamin D. These include fish, eggs, and mushrooms.

There are also artificially fortified sources such as some cereals, orange juice, cow's milk and dairy products. However, not all of these are available in Bulgaria. Infant formulas also usually contain added vitamin D.

Fish

Fish, especially oily fish, is the best-known dietary source of vitamin D. For example, cod liver oil was one of the first methods used to prevent rickets in children. This is the type of fish oil with the highest vitamin D content.

However, cod liver oil is also high in another fat-soluble vitamin, vitamin A (retinol). Just one tablespoon contains over 4 times the recommended dietary allowance of retinol, and prolonged use can lead to toxicity.

Other types of fish rich in vitamin D include salmon, herring, sardines, mackerel, and tuna. Salmon is usually the better choice because it contains much less mercury than some types of mackerel and tuna.

However, Black Sea mackerel has good levels of vitamin D and a very low risk of mercury.

However, studies show that there is a huge difference between wild and farmed salmon in terms of vitamin D content – farmed salmon has 4 times lower levels of vitamin D. [30].

Eggs

Eggs, and more specifically the yolks, also contain a certain amount of vitamin D. However, its level strongly depends on how the chickens are raised, as well as on their diet.

Studies show that even when chickens are given food with the same amount of vitamin D, chickens that roam freely outside have 3-4 times higher vitamin D content in their eggs. [31].

That's why consuming whole eggs from free-range hens can also be an effective way to increase your vitamin D intake.

If you have concerns about your cholesterol levels, consult your doctor before increasing your egg yolk intake. 

Research shows that increasing dietary cholesterol intake does not affect blood cholesterol levels in most people. Studies show that only 15-25% of people are hyperresponders to cholesterol and consuming more cholesterol will lead to changes in their lipid profile. [32]. 

Even if you are, scientists do not report increased cardiovascular risk in hyperresponders.

Mushrooms

Mushrooms are also a source of vitamin D, but not D3 and on D2, which is the most common choice among vegans, but is not optimal for humans. 

Furthermore, the level of the vitamin depends largely on whether the mushrooms are wild or farmed, as well as on the method of cultivation.

Unfortunately, most mushrooms are grown in the dark, which completely deprives them of any vitamin D. On the other hand, consuming wild mushrooms carries risks of poisoning.

According to studies, modern cultivation methods using ultraviolet light can increase the vitamin D content in mushrooms to levels equivalent to those in wild mushrooms. [33].

What is the most reliable source of vitamin D?

The most natural way to increase your vitamin D levels is through exposure to direct sunlight. However, this method is often unreliable due to various factors, including season, genetics, age, and more.

Additionally, excessive exposure to sunlight is a risk factor for serious conditions such as skin cancer due to exposure to ultraviolet rays.

Given the highly variable amounts of vitamin D in different food sources, as well as the high incidence of vitamin D deficiency, experts widely recommend taking a vitamin D supplement. [34].

There are currently two main forms of vitamin D available as a supplement – vitamin D3 and vitamin D2.

According to a meta-analysis of 7 studies, vitamin D3 has better bioavailability than vitamin D2 and leads to a more reliable increase in serum concentrations [35].

In addition, D2 It appears to be a less stable form of the vitamin, and so researchers suggest it may have a short shelf life as a supplement. [36].

Therefore, the majority of experts recommend vitamin D supplements.3, to increase serum levels more reliably.

What is the best way to absorb vitamin D?

Vitamin D supplementation is only effective if it is absorbed properly. To increase vitamin D absorption, you need to do 3 things:

• take it with a meal rich in healthy fats, as vitamin D is a fat-soluble vitamin
• avoid foods and medications that block the absorption of the vitamin
• to choose a more digestible form

Taking the vitamin with food rich in healthy fats ensures the release of bile acids into the digestive tract, which is important for proper absorption of vitamin D.

That's why most experts recommend taking a vitamin D supplement with the largest meal of the day, which for most people is lunch or dinner.

What can interfere with the absorption of vitamin D?

Fiber is an important part of any healthy diet as it aids digestion, lowers cholesterol, improves blood sugar control and reduces the risk of colon cancer.

However, it is important to avoid taking vitamin D with other supplements that may contain fiber, such as many weight loss and digestive products.

Additionally, prolonged use of several medications can lead to reduced absorption or changes in vitamin D metabolism and therefore deficiency. Examples of this include:

• Laxatives (bisacodyl)
• Corticosteroids
• Cholesterol-lowering medications (such as cholestyramine and colestipol)
• Seizure control medications (such as phenobarbital and phenytoin)
• Anti-tuberculosis drug (rifampin)
• Weight loss medications (orlistat)

How to quickly increase vitamin D levels?

The most reliable source of vitamin D that can help you quickly raise your serum levels is a vitamin D supplement.3. Most guidelines recommend supplementing with at least 15mcg (600 IU) daily. [37], [38], [39].

However, these levels may not be enough for people with severe deficiency to reach adequate serum levels of vitamin D. Therefore, most experts recommend 1,000 to 4,000 IU of the vitamin daily.

In addition to taking supplements daily, taking a bolus dose once a week or even once a month is also an option.

Studies have shown that this method can also lead to sustained increases in serum vitamin D levels. However, daily supplementation appears to produce comparable increases that occur more quickly than a single bolus dose. [40].

That is why it is more appropriate to choose daily dosing if you want to correct your deficiency more quickly.

Additionally, scientists report that the physiological limit for vitamin D intake is 10,000 IU per day, which is equivalent to prolonged whole-body exposure to direct sunlight. [41].

Taking 10,000 IU of vitamin D or more can be toxic. Toxicity is thought to occur when supplement doses of more than 10,000 IU per day are taken for more than 3 months or more than 300,000 IU in 24 hours. [42].

How long does it take to correct vitamin D deficiency?

The dosage and form of the supplement are not the only factors that determine how quickly you can restore your vitamin D levels.

According to scientists, the period needed to correct vitamin D deficiency depends on several other factors. [42]. These include:

• your baseline vitamin D levels
• your age
• season and sun exposure
• your skin pigmentation
• genetic variations
• Are you taking any medications?
• your body fat percentage and body composition
• your overall diet

So don't forget to measure your vitamin D levels and consult a doctor first. Depending on your baseline vitamin D levels and the other factors listed above, your doctor can determine the most optimal dose for you.

Which vitamin D is best?

When choosing a dietary supplement, it is best to choose a product that contains both vitamin D3 and vitamin K2.

Vitamin K is actually a group of fat-soluble vitamins that play an important role in the human body. These vitamins control blood clotting, as well as the deposition of calcium in various tissues, including bones.

Namely vitamin K2 is the best option for humans by supporting the action of vitamin D for healthy bones. According to studies, the combination of vitamin D3 and K2 may have synergistic benefits for bone density [43]. 

In addition, vitamin K2 may reduce the risk of calcium deposits in blood vessels, which is a potential risk factor for cardiovascular disease. 

That's why the combination of vitamin D3 and vitamin K2 will help direct calcium to your bones and reduce the potential risks of high vitamin D levels.