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Is Vitamin D Your Key to Unlocking a Healthy Immune System?

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Vitamin D and the Immune System

In the past couple of years, we’ve become keenly aware of how important it is to have a strong, healthy immune system. As it turns out, a basic vitamin we’re all familiar with – the “sunshine vitamin” – plays a key role in supporting and maintaining a healthy immune system.

Vitamin D’s Role in Your Immune System

Vitamin D is an important player in your body’s immune system, helping modulate both your innate and adaptive immune responses.

  • The innate immune response is your body’s first line of defense. It detects all foreign invaders such as viruses, bacteria, parasites and toxins, activating cells to attack and destroy the intruders.
  • The adaptive immune response is your body’s second line of defense. Triggered by the innate immune cells, the adaptive cells recognize the specific invader then multiply to fight it off and provide protection against its return.

Remarkably, in addition to activating immune cells to combat invaders, vitamin D also has been found to help those cells maintain their healthy state rather than becoming overactive and attacking healthy tissue.

Some additional evidence of vitamin D’s ability to support the immune system includes:

  • An article in the August 2011 issue of the Journal of Investigative Medicine, reported that a vitamin D deficiency is associated with increased susceptibility to infection.
  • In 2009, the National Institutes of Health warned that low vitamin D levels were associated with colds and flu, noting that “vitamin D may play a role in helping the immune system ward off respiratory diseases like the common cold.”

More Vitamin D Benefits

Vitamin D is perhaps best known for its contribution to bone health. It plays an important role in your body’s ability to absorb calcium. When vitamin D levels are low, calcium concentrations are inadequate, leaving you more vulnerable to bone-related disorders. Additionally, vitamin D has a positive effect on other vitamins and minerals that support bone health, like magnesium, phosphorus and vitamin K.

Other vitamin D benefits include: support for a healthy cardiovascular system and healthy blood sugar levels, mood support, skin health and brain health – supporting memory, concentration and learning.

Are You at Risk for a Vitamin D Deficiency?

As it turns out, almost everyone is at risk of having a vitamin D deficiency. A 2009 epidemiological study found that an astounding 77% of Americans have insufficient levels of vitamin D. The numbers are even higher in Europe and higher still in the Middle East, where people have darker skin pigmentation and women especially tend to stay covered when outdoors.

Although virtually everyone has some risk, following are specific risk factors for a vitamin D deficiency:

  • Being over 50 – As you age, your skin cannot synthesize vitamin D as efficiently and your kidneys are less able to convert it to its active hormone form.
  • Limited sun exposure – If you’re homebound, wear clothing that covers most of your skin, or live in northern latitudes that get little sunlight part of the year, it’s unlikely that you get adequate amounts of vitamin D.
  • Wearing sunscreen – While wearing sunscreen or sunblock is recommended to prevent skin cancer, unfortunately, it also blocks the UVB rays your body needs to produce vitamin D naturally.
  • Having dark skin – The pigment melanin, which results in darker skin, also reduces the skin’s ability to produce vitamin D from exposure to sunlight.
  • Fat malabsorption disorders – Vitamin D is fat soluble and therefore requires some dietary fat in the gut for absorption. Some medical conditions associated with fat malabsorption include some forms of liver disease, cystic fibrosis and Crohn’s disease.
  • Tobacco smoking – Tobacco smoking is associated with significantly reduced vitamin D levels.
  • Obesity – Greater amounts of subcutaneous fat sequester more of the vitamin D and alter its release into the circulation.
  • Gastric bypass surgery – Part of the upper small intestine where vitamin D is absorbed is bypassed, which may lead to inadequate levels.

How to Tell if You Have a Vitamin D Deficiency

The only way to know for sure if you are deficient in vitamin D is to have a blood test that measures serum 25(OH)D concentrations. 25(OH)D or 25-hydroxyvitamin D is a metabolite of vitamin D.

There is considerable disagreement among experts as to exactly what normal and ideal 25(OH)D levels should be. Though norms will vary between labs, the following chart will give you a general idea of what to look for:

25(OH)D Concentrations
(ng/ml stands for nanograms per milliliter)
Severely Deficient< 8 ng/ml
Deficient8 – 19 ng/ml
Insufficient20 – 29 ng/ml
Sufficient30 – 49 ng/ml
Optimal50 – 99 ng/ml
Excessive100 – 150 ng/ml
Potentially toxic>150 ng/ml


Sources of Vitamin D

Sunlight – Vitamin D has long been called the “sunshine vitamin” because it is naturally produced when skin is exposed to sunlight’s UVB rays. In fact, exposure to sunlight is the only natural way to get sufficient amounts of vitamin D. That sounds simple enough, except that most people do not get enough exposure to sunlight on a regular, year-round basis to maintain optimum levels of vitamin D. Unless you live in a climate that is sunny most of the year, and you get at least 15 minutes of direct midday sunlight every day, there’s a good chance you’re not getting all the vitamin D your body needs.

Diet – Trying to get your vitamin D through food is not the best option because, with the exception of oily fish and fish-liver oil, vitamin D does not naturally occur in most foods. Some food items, like milk and other dairy products, orange juice, nut milks and breakfast cereals, have been fortified with small amounts of vitamin D. However, it is virtually impossible to get adequate amounts of vitamin D through your diet. For example, it would take 5 cans of tuna, 10 glasses of milk, or up to 17 cups of breakfast cereal to get just 1000 IU of vitamin D.

Supplementation – Because it can be difficult to regularly get adequate amounts of vitamin D from natural sources, for most people supplementation is the best and most practical solution. Vitamin D supplements are inexpensive and safe in reasonable doses.

Which Form of Vitamin D Is Best?

There are two main types of vitamin D – vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). D3—the form your body naturally produces from sun exposure—is the one your body prefers because it is more easily absorbed and utilized. D2—made by irradiating yeast and other molds—is not nearly as effective because your body has to convert it to D3 before it can be used. In fact, D3 is estimated to be four times more effective in humans than D2.

How Much Vitamin D3 Should You Take?

There’s no simple answer to the question of how much vitamin D3 you should take. Recommended dosages vary significantly depending on who you ask. Plus there are a number of variables to consider. If you are currently deficient in vitamin D or have one or more risk factors, you may require a higher dose than someone who is just trying to maintain an already healthy vitamin D level.

In addition to differing opinions about recommended doses, there also continues to be a great deal of disagreement among medical professionals as to the maximum safe dosage. While some feel that the limit should be around 5,000 IU/day, other experts insist that doses up to 10,000 IU/day are safe.

One protocol successfully used by many clinicians for patients who are deficient in vitamin D is to take 50,000 IU/week for approximately three months or until your 25(OH)D levels are in the optimal range; then switch to a maintenance dose of 2,000 to 5,000 IU/day.

Of course, always talk with your doctor about this or any supplement you are considering. And the best way for you and your doctor to ensure you are taking the right dose of vitamin D for you is to have your 25(OH)D serum levels checked regularly—ideally every three months—at least until you reach and maintain an optimal level.


Research clearly demonstrates that vitamin D3 is very beneficial for your immune system as well as your overall health. Plus, it’s inexpensive and safe when taken responsibly, so there’s really no downside.

Karen Lee Richards is ProHealth’s Editor-in-Chief. A fibromyalgia patient herself, she co-founded the nonprofit organization now known as the National Fibromyalgia Association (NFA) in 1997 and served as its vice-president for eight years. She was also the executive editor of Fibromyalgia AWARE magazine. After leaving the NFA, Karen served as the Guide to Fibromyalgia and Chronic Fatigue Syndrome for the New York Times website About.com, then worked for eight years as the Chronic Pain Health Guide for The HealthCentral Network before coming to ProHealth. To learn more about Karen, see “Meet Karen Lee Richards.


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By ProHealth-Editor

Karen Lee Richards is ProHealth’s Editor-in-Chief. A fibromyalgia patient herself, she co-founded the nonprofit organization now known as the National Fibromyalgia Association (NFA) and served as its vice-president for eight years. She was also the executive editor of Fibromyalgia AWARE, the very first full-color, glossy magazine devoted to FM and other invisible illnesses. After leaving the NFA, Karen served as the Guide to Fibromyalgia and Chronic Fatigue Syndrome for the New York Times website About.com, and then for eight years as the Chronic Pain Health Guide for The HealthCentral Network.To learn more about Karen, see “Meet Karen Lee Richards.”

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