Vitamin D: Benefits, Immune Support and How Much You Need

Vitamin D is a fat-soluble vitamin your body needs for strong bones, healthy muscles and a balanced immune response [1]. Decades of micronutrient research include vitamin D3 as one member of a team of nutrients that work together [2].

What is vitamin D?

Vitamin D is a fat-soluble vitamin that your skin makes when it's exposed to sunlight. It's also found in some of the foods we eat, such as fatty fish, egg yolks and fortified milk, and yes, in supplements [1].

Vitamin D comes in two main forms: D2 (ergocalciferol) and D3 (cholecalciferol). Comprehensive micronutrient formulations favor vitamin D3, the same form your skin produces [3]. Two organs in your body, your liver and your kidneys, convert vitamin D into its active form, calcitriol, which acts more like a hormone than a typical vitamin [1].

What does vitamin D do for the body?

Vitamin D's best-known job is helping your body absorb calcium and keep it in balance. That's why vitamin D3 is often paired with calcium and magnesium [1] [4].

Vitamin D is important to four things inside the human body: the bones, the muscles, the cells and the immune system. Let's take each one individually.

• The bones: Vitamin D supports bone growth and remodeling, and helps keep bones strong [1].
• The muscles: Vitamin D supports normal muscle function [1].
• The cells: Many tissues carry vitamin D receptors, and vitamin D helps regulate genes involved in cell growth and renewal [1].
• The immune system: Vitamin D helps regulate both the first-line and the targeted arms of immunity [1] [9].

Why is vitamin D important for the human body?

Without enough vitamin D, or the right amount of it, the body can't use calcium effectively, and over time the bones can become thin, soft or brittle [1].

Low vitamin D is more common than many people realize. Most Americans get less than the recommended amount from food alone [1], and about 1 in 4 have blood levels that are low or borderline [5]. Few foods contain much of it, and many people today get very little sun.

Research links two processes to declining health with age: increased oxidative stress, which is damage from excess free radicals, and chronic inflammation [2]. Vitamin D3 is a core part of comprehensive micronutrient mixtures designed to help the body manage both, alongside antioxidants, B vitamins and minerals [6] [7] [8]. Vitamin D does its best work as part of the team, not by itself.

How does vitamin D support immune function?

Vitamin D supports immune function in two ways: it helps your immune cells fight off germs, and it helps keep inflammation in balance [1] [9]. In fact, people with low vitamin D tend to be more prone to infections [9].

Think of your immune system as having two jobs: responding strongly when a threat shows up, and calming back down once the job is done. Vitamin D helps with both. Let's look at how.

• First-line (innate) defense: This is your body's rapid-response team. Vitamin D helps immune cells called macrophages make natural germ-fighting proteins, such as cathelicidin [10].
• Targeted (adaptive) defense: This is the part of your immune system that learns and remembers specific threats. T cells, B cells and other immune cells carry vitamin D receptors, and they can even make active vitamin D themselves. That lets vitamin D help guide how they behave, right where they're working [9].
• Balanced inflammation: Inflammation is a normal part of a healthy immune response, but too much of it works against you. Vitamin D helps keep inflammation in check, so the response stays in proportion [1] [9].

Oxidative stress, inflammation and immune health are all closely connected. That's why comprehensive micronutrient formulations are designed to address oxidative stress and inflammation together, rather than one at a time [2].

Getting the most from vitamin D

If you want to get the most out of vitamin D, here are four things the research points to.

• Choose D3: Vitamin D3 raises the vitamin D in your blood more than D2 does, and keeps it there longer [1]. It's also the form used in research-based micronutrient formulations [3] [4] [11].
• Keep amounts moderate: These formulations use roughly 400 to 1,000 IU of vitamin D3 a day [3] [11] [12]. The Micro Daily EMF formula, for example, provides 20 mcg (800 IU) of vitamin D3 a day, 100% of the Daily Value [14]. That lines up well with the official recommendation of 600 to 800 IU a day for most adults [1].
• Don't take it alone: Single nutrients taken by themselves tend to give inconsistent results. Vitamin D works best when it's combined with antioxidants, B vitamins and minerals [2].
• Take your formula twice a day: Comprehensive formulas are designed to be split into a morning dose and an evening dose, because many of their nutrients leave the body within hours [13]. Vitamin D itself is stored in your body and stays in your blood for weeks [1], so it simply comes along for the ride.

One last thing to keep in mind: with vitamin D, more isn't better. Because it's fat-soluble, your body stores it, and very high intakes can build up over time and cause harm [1].

Frequently asked questions about vitamin D

How much vitamin D do I need each day?

Most people ages 1 to 70 need 600 IU (15 mcg) a day, and adults over 70 need 800 IU (20 mcg). Infants need 400 IU (10 mcg). For adults, the safe upper limit is 4,000 IU (100 mcg) a day from all sources combined [1].

What's the difference between vitamin D2 and D3?

Both forms raise the vitamin D in your blood, but D3 raises it more and keeps it there longer. D3 is the form your skin makes, while D2 is made from yeast and is also found in some mushrooms [1].

What foods are high in vitamin D?

Fatty fish are your best natural sources. A 3-ounce serving of cooked sockeye salmon has about 570 IU, and the same amount of farmed rainbow trout has about 645 IU. One tablespoon of cod liver oil has about 1,360 IU. Fortified milk and plant milks give you about 100 to 144 IU per cup, and one egg about 44 IU [1].

Who is most likely to be low in vitamin D?

The groups most at risk are breastfed infants, older adults, people who get little sun, and people with darker skin. People with conditions that limit fat absorption, such as Crohn's or celiac disease, and people with obesity or who have had gastric bypass surgery are also at higher risk [1].

What happens if you don't get enough vitamin D?

Over time, low vitamin D can lead to soft, weak bones. In children this is called rickets, and in adults it's called osteomalacia, which can cause bone pain and muscle weakness [1].

Can you take too much vitamin D?

Yes. Very high intakes, almost always from supplements, can push the calcium in your blood too high. That can cause nausea, vomiting, muscle weakness and kidney stones [1]. Staying at or below the upper limit helps you avoid this.

Explore more micronutrients

Vitamin D works alongside other nutrients. Learn more about magnesium, iron, vitamin B12, calcium, zinc, potassium and folate.

Key sources: NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals [1]; Aranow C, "Vitamin D and the Immune System," Journal of Investigative Medicine, 2011 [9]; Prasad KN, Micronutrients in Health and Disease, CRC Press, 2019 [2]. Every numbered citation links to its full entry on our References page.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Talk with your healthcare provider before starting any supplement, especially if you are pregnant, nursing, taking medication or have a medical condition.