Why We Need Vitamin D3 All Year Round

Vitamin D often causes confusion: how can it be found in food but also in sunlight? And why is it called "Vitamin" D when it’s actually a hormone? Here’s what vitamin D3 is, its role in the body, and the best sources.

Table of Contents

What Is Vitamin D3?

First of all, vitamin D isn’t actually a vitamin, but a hormone—more precisely, a prohormone, which is a precursor to a hormone and plays a role in many biological processes.

So why is it called a vitamin? When it was discovered in the early 20th century during research for remedies, it wasn’t known that the body could produce it, unlike a typical vitamin. Initially classified as the fourth vitamin, scientists later realized that the body stores a precursor of vitamin D in the skin, which it then converts into active vitamin D3 through UVB radiation.

Vitamin D3, also known as cholecalciferol, is the form of vitamin D that our bodies produce. Since it’s still referred to as a vitamin, it’s the only one the body can synthesize. By the way, there’s also vitamin D2, a form of vitamin D synthesized in the human body from plant sterol derivatives found in food. However, this form is considered less effective as a supplement than vitamin D3.

How Does the Body Produce Vitamin D3?

To understand the body's production of vitamin D3, we first need to know what UV rays are. Ultraviolet rays are a type of solar radiation that can be divided into ultraviolet A (UVA) and ultraviolet B (UVB) rays. While UVA rays penetrate deep into the skin and often cause damage, UVB rays don’t penetrate as deeply and are responsible for vitamin D production. When exposed to sunlight, the cholesterol in our skin cells absorbs the UVB rays, providing the energy needed for vitamin D synthesis in the skin.

Why Is Vitamin D3 So Important?

Vitamin D3 is essential because it plays a role in many biological processes, especially in bone health. Without vitamin D3, our intestines wouldn’t properly absorb calcium and phosphate during digestion, and these important minerals wouldn’t benefit your bones.

It’s worth noting that many organs and tissues in the body have vitamin D receptors, suggesting important functions beyond bone health. These include muscles, kidneys, parathyroid glands, and the skin.

It also supports the immune system, contributes to cardiovascular health, and helps maintain muscle strength. Moreover, it influences our mental health and mood by supporting the production of neurotransmitters like serotonin and has anti-inflammatory effects.

How Much Vitamin D3 Do You Need Daily?

The unique aspect of vitamin D3 is that our body produces it through UVB light exposure on the skin. However, if our skin is exposed to insufficient sunlight, the body’s production may not be enough.

The recommended daily intake is around 20 µg, but this is highly individual: for example, people with darker skin may need 10 to 50 times the UV dose compared to fair-skinned individuals, while vitamin D production in 70-year-olds can be 3 to 5 times lower than in younger people.

In northern latitudes, the sun is strong enough to reliably stimulate vitamin D production in the skin for only about 3 to 4 months a year (usually from April to September). You also need to consider your actual sun exposure—how often are you outdoors in the sun each day?

Which Foods Contain Vitamin D3?

You can supplement your body’s vitamin D3 intake with the following foods:

These foods contain vitamin D3.
These foods contain vitamin D3.

What Are Possible Symptoms of Vitamin D3 Deficiency?

A Vitamin D deficiency can manifest through bone pain, muscle weakness, increased susceptibility to infections, and chronic fatigue. Mood swings, hair loss, and delayed wound healing can also indicate a deficiency. If you’re concerned about a vitamin D deficiency, your doctor can provide guidance.

What Should You Consider When Supplementing with Vitamin D3?

When supplementing with vitamin D3 through foods or supplements, it’s important to note that vitamin D is fat-soluble, meaning it’s best absorbed with a fat source to increase bioavailability. Ideally, you should take vitamin D3 with a meal that contains healthy fats, such as olive oil, avocado, or nuts, or with a supplement that provides vitamin D3 in oil.

It’s also scientifically proven that vitamin D and vitamin K2 together support cardiovascular health, help maintain bone density, and promote normal immune function. The combination of vitamins D3 and K2 offers greater benefits together than either nutrient alone—this concept is known as nutrient synergy. For this reason, it makes sense to use a supplement that combines vitamin D3 and vitamin K2.

Can You Take Too Much Vitamin D3?

In theory, it is possible to take too much vitamin D3. Symptoms of an overdose may include nausea, vomiting, loss of appetite, weakness, fatigue, increased thirst, and frequent urination. However, these cases are rare, as very high amounts of the vitamin would be necessary. You can also rest assured that overproduction from too much sun exposure is unlikely.

Does Sunscreen Prevent Vitamin D Absorption?

In short: yes. Sunscreen can impair the production of vitamin D in the skin because it blocks the UVB rays needed to activate the vitamin precursor in the skin. Studies have shown that high SPF can significantly reduce vitamin D synthesis. Nonetheless, it’s important to use sunscreen to prevent skin cancer and other UV-induced skin damage. To avoid a vitamin D deficiency, you can consider alternative sources such as supplements or fortified foods.

It’s also worth noting that "supplementing" sun exposure through tanning beds isn’t necessarily helpful, as most tanning beds primarily use UVA rays. However, only UVB radiation is needed to stimulate the body’s production of vitamin D3.

At a Glance

  • 01.

    Vitamin D3 plays a crucial role not only in bone health but also in immune function and muscle maintenance.

  • 02.

    Foods like salmon, herring, eggs, and mushrooms are good sources of vitamin D3.

  • 03.

    Our bodies can produce this hormone themselves, but supplements through diet and nutritional supplements can be beneficial in cases of low sunlight exposure.

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Immune System

1: Copper, folate, selenium, zinc, and vitamins A, B12, B6, and C contribute to the normal function of the immune system.

Metabolism

2: Vitamins C, B6 and B12, as well as thiamine, riboflavin, niacin, biotin, pantothenic acid, calcium, phosphorus, copper, and manganese contribute to normal energy-yielding metabolism. Biotin, zinc, and chromium contribute to normal macronutrient metabolism. Vitamin A and riboflavin contribute to normal metabolism of iron. Zinc contributes to normal acid-base metabolism.

Healthy Cells

3: Vitamins E and C, as well as riboflavin, zinc, copper, manganese and selenium, contribute to the protection of cells from oxidative stress. Zinc contributes to normal DNA synthesis. Phosphorus contributes to normal function of cell membranes.

Mental Performance; Mental Focus; Nervous System; Psychological Function

4: Vitamins C, B6, B12, riboflavin, niacin, pantothenic acid and folic acid contribute to the reduction of tiredness and fatigue. Pantothenic acid contributes to normal mental performance. Zinc contributes to normal cognitive function. Vitamins C, B6, B12, thiamine, riboflavin, niacin, biotin, and copper contribute to normal functioning of the nervous system. Thiamine, niacin, vitamin B6, vitamin B12, biotin, folate, and vitamin C in AG1 contribute to normal psychological function.

Healthy bones

5: Calcium contributes to the maintenance of normal bones. Protein, phosphorus, zinc, and manganese contribute to the maintenance of normal bones. Vitamin C contributes to normal collagen formation for the normal function of bones.

Cardiovascular System

6: Thiamine contributes to the normal function of the heart. Vitamins B6 and B12 contribute to normal red blood cell formation. Vitamin C contributes to normal collagen formation for the normal function of blood vessels.

Skin, hair, nails

7: Vitamin A, riboflavin, niacin, biotin and zinc contribute to the maintenance of normal skin. Vitamin C contributes to normal collagen formation for the normal function of skin. Biotin, zinc and selenium contribute to the maintenance of normal hair. Copper contributes to normal skin and hair pigmentation and to normal connective tissue. Selenium and zinc contribute to the maintenance of normal nails.

Hormonal Health

8: Vitamin B6 contributes to the regulation of hormonal activity. Pantothenic acid contributes to normal synthesis and metabolism of steroid hormones, vitamin D, and some neurotransmitters. Zinc contributes to the maintenance of normal testosterone levels in the blood. Selenium contributes to normal thyroid function and normal spermatogenesis. Zinc contributes to normal fertility and normal reproduction. Chromium contributes to the maintenance of normal blood glucose levels.

Digestion

9: Calcium contributes to the normal function of digestive enzymes. Biotin contributes to the maintenance of normal mucous membranes (e.g., intestinal mucosa).

Muscles

10: Calcium contributes to normal muscle function. Proteins contribute to the maintenance of muscle mass and an increase in muscle mass.

Healthy eyes

11: Vitamin A, riboflavin and zinc contribute to the maintenance of normal vision.

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