Vitamin D: A Summary of What the Research Reveals, and How To get Enough of it.
Vitamin D is Essential to Many Vital Functions

A nutrient essential to many immune functions is Vitamin D. Approximately 41% of adult Americans are deficient in Vitamin D [1], despite it being produced naturally via an interaction which occurs during exposure to UV light (sunlight) [2]. Numerous studies have shown Vitamin D to play an active role in supporting and maintaining the vital processes the body requires to fight disease. There are many studies showing a link to Vitamin D deficiency as a possible cause for a broad spectrum of ailments [3][4].

Vitamin D Regulates Mineral Absorption Deficiency May Result in Weak Bone Structure One Billion People Worldwide Have Low levels of Vitamin D



Chronic Infections

Muscle pain

Recurring Illness

Reduced Bone Mass

Hair Loss


Weight Gain

Risk Factors Attributing to Deficiency

With more people working indoors or from home, fewer people are absorbing the amount of sunlight required to maintain adequate levels of Vitamin D. It is estimated that approximately one billion people worldwide have insufficient amounts of Vitamin D [8]. The causes of deficiency vary by demographic, however the sources for obtaining sufficient quantities of Vitamin D are essentially through adequate sun exposure and diet. Dietary sources are limited for many, and certain additional risk factors contribute to these findings as well.

What Exactly Is Vitamin D?

Vitamin D is called a ‘vitamin’ because it is a necessary substance for processes to occur in the body. More specifically, Vitamin D is a type of hormone called a secosteroid. It is fat soluble and is primarily important in two forms, ergocalciferol and cholecalciferol- Vitamins D2 and D3, respectively. Both ergocalciferol and cholecalciferol are inactive when initially ingested, whether it be ingested in the form of a supplement, a food in which it is found naturally, or in food which has been artificially fortified to contain either compound. Oral ingestion of Vitamin D will only increase serum levels once the digestive system has passed it through the liver and kidneys, passing what are known as metabolites into the bloodstream, where dispersion to areas it is needed is made possible. When ingested, Vitamin D first passes through the liver and is processed into a form that can be stored. Later, the kidneys process the storage form and convert it into the metabolites which the body is then able to use [5]. The difference between Vitamin D2 and D3 is molecular and affects the way D is metabolized. The metabolic process can be summarized to say that there is both a better binding ability, and also, more metabolic forms- from ingesting Vitamin D3 rather than D2. Studies show that D3 is twice as effective as D2, in regard to raising blood levels of Vitamin D [6]. A primary function of Vitamin D is the regulation and absorption of calcium, magnesium, and phosphate [7].

There are only a few foods which naturally contain Vitamin D. These foods include egg yolks, bovine or fish livers, certain species of fish with high fat content, as well as some fungi. Other foods, which are more commonly available, are sometimes fortified with Vitamin D artificially. These may include dairy products such as milk, fortified yogurt, infant formulas, cereals, or dairy substitutes to which it has been added.

Vitamin D Insufficiency and Deficiency are Defined by the Amounts Found in Blood tests.

Deficiency is defined as being less than 20 nanograms per milliliter (20ng/mL)

Insufficiency is Defined as a Range of 21-29 ng/mL [9]

The risk factors of acquiring a Vitamin D deficiency go beyond diet. There is no single cause associated with deficiency, however there may be a greater risk as a result of various lifestyles and/or underlying conditions. Some common risk factors include [10]:

Common Risk Factors of Deficiency


Taking Certain Medications Like Statin Drugs or Steroids

Working Overnight

Having a Dark Skin Tone

Lack Fish/Fortified Dairy Products in Diet

Older People are More Susceptible

Living in a Region that Gets Little Sunlight

People who are older seem to be more susceptible to having insufficient or deficient serum levels of Vitamin D. The same applies to those who live in areas which don't get much year-round sunlight. Certain medications, such as steroids or statin drugs, affect serum levels and can also be a risk factor [13]. Deficiency risk is also elevated in those who suffer from certain medical conditions [13][14][15], such as:

Diseases Which Contribute to Deficiency Risk

Chronic Kidney or Liver Disease

Celiac Disease


Crohn’s Disease

Other Diseases Which Impair Nutrient Absorption

Vitamin D and the Immune System

Immune health is an area where Vitamin D is being studied for the central role it plays in aiding immune function. Studies show that Vitamin D directly interacts with cells that respond to infection [16].

Low serum levels of Vitamin D may be linked to the frequent occurance of colds and respiratory infections [18][19] as well. A number of studies have found evidence that taking a daily dose of up to 4,000 IU of Vitamin D may reduce the risk of respiratory infections [20][21][22].


Fatigue can be a symptom of a weakened immune system [17], and low serum levels of Vitamin D may be a potential cause. Exhaustion upon waking up, or feelings of tiredness even after getting appropriate rest could be a sign that immune system function is impaired

There can be many causes for being tired. One of those causes may be low or deficient levels in vitamin D. Fatigue symptoms have been linked to Vitamin D deficiency in one study, in which the study group consisted of 480 older adults [23]. Another study involved 39 children, and the data linked low levels of Vitamin D to a shorter duration of sleep, later bedtimes, and a lower quality of sleep [24]. People that have a deficiency may benefit from taking a Vitamin D supplement. Several studies report data which suggest that, with a supplement, the severity of fatigue symptoms may be reduced in people with deficiency [25][26].

Vitamin D deficiency, especially in older adults, has been linked to depression, although some reports are mixed [27][28][29]. The studies surrounding the correlation of Vitamin D deficiency and depression are conflicting, however some reports have suggested supplements helped relieve depression symptoms [30][31][32][33]. More research is needed to determine exactly what links exist between depression and Vitamin D.


Inflammatory Response to Infection

Inflammation, and the role Vitamin D has in controlling inflammatory responses to infection, may be relevant to healing properly. Low levels of Vitamin D in the blood may contribute to injuries healing slowly. A study conducted in test tube samples suggests that Vitamin D increases production of chemicals that are important to new skin formation [34]. Additionally, four studies have been analyzed in a review which discovered that deficiency in Vitamin D compromised some factors related to recovery in dental surgery patients [35]. More research is needed to fully understand the correlation of these findings [36].

Vitamin D and Bone Health

Vitamin D plays a central part in the absoption of calcium, which is critical to a healthy bone structure. Low bone density is often attributed to a loss of minerals and calcium, or poor absorption. Vitamin D aids the absorption of calcium when taken together [37][38].

Adults who are older, especially women, are at increased risk for bone fractures when their bone density is low. A large study comprising of over 1,100 menopausal and post-menopausal women found that there was a strong correlation between low bone density and low levels of Vitamin D [39].

While these studies report a corellation of the data, another study showed no improvement in bone density after serum levels improved with supplementing [40].

Summary of Findings

Vitamin D is a fat soluble vitamin - which has a significant role - in absorbing and regulating the levels of magnesium, phosphorus, and calcium. While it has proven to be crucial in many biological processes, more data is needed to fully understand how these findings correlate with our health. If you believe you may be at risk of Vitamin D deficiency, you should consult your doctor for advice and testing which will determine the supplement dosing right for you.








































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