Everything You Need to Know About Vitamin D

The sunshine vitamin is essential to our health, but some of us don’t get enough. Find out what vitamin D is, what it does for the body, how to get it, and if you can have too much.

By Anna Nordseth; Medically Reviewed by Dr. Ahmad Talha Azam
Jan 26, 2024 5:00 PMApr 4, 2024 7:24 PM
Young Woman is holding Vitamin D Capsule. Sun and blue Sky.
(Credit:Food Impressions/Shutterstock)


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In an era where indoor lifestyles and office-centric work environments have become the norm, a silent health concern looms large: vitamin D deficiency. Vitamin D is crucial for bone health, immune function, and overall well-being. 

However, modern lifestyles that keep us indoors don't lend themselves to getting enough sun for sufficient vitamin D production. As a result, experts estimate that nearly 50 percent of Americans aren't getting enough vitamin D.

Despite its significance, questions remain: How much is enough? Can supplements effectively address a deficiency? Is there a benefit to taking more than the recommended amount?

The answers to these questions remain a topic of research and debate among researchers and doctors.

What Is Vitamin D?

Vitamin D, also known as calciferol, is a fat-soluble vitamin essential for various body functions. Colloquially known as the "sunshine vitamin," our bodies make vitamin D when our skin is exposed to sunlight — a built-in production system that hints at just how essential vitamin D is for our health

What Does Vitamin D Do for the Body?

​​Vitamin D regulates calcium and phosphorus levels in the blood. These two essential minerals then go on to build strong bones and carry out myriad other bodily functions.

Even with adequate vitamin D, we only absorb between 30 and 40 percent of the calcium from food; without enough vitamin D, that number drops to only 10 or 15 percent.

Vitamin D is fat-soluble, meaning it's absorbed with dietary fats and stored in fat tissue and the liver, ready for release when our body signals the need.

Read More: Full Vitamin D Deficiency Guide

Why Is Vitamin D Important For Bone Health?

Over a century ago, researchers uncovered the role of vitamin D in bone health; the initial breakthrough found that vitamin D could cure rickets — a debilitating bone disease in children.

This discovery led to the fortification of staple foods like milk and orange juice that we see in grocery stores today.

Vitamin D deficiency can have similar effects on adults by causing a condition called osteomalacia, where bones do not mineralize properly, making them more susceptible to breaks and fractures.

What Are the Benefits of Vitamin D?

The benefits of vitamin D include:

  • Strengthening bones and teeth

  • Supporting immune, brain, and nervous system health

  • Regulating insulin levels and aiding diabetes management

  • Supporting lung function and cardiovascular health

  • Influencing the expression of genes involved in cancer development

What Has Vitamin D?

While our bodies can produce it through sun exposure, there are several other sources to ensure adequate intake, especially in situations where sun exposure is limited. Here's a look at the best sources:


Certain foods are natural sources of vitamin D, including fatty fish like salmon and mackerel, fish liver oils, and small amounts in beef liver, cheese, and egg yolks.


Sun exposure is a primary natural source of vitamin D. When your skin is exposed to sunlight, it produces vitamin D naturally.


Fruits generally contain minimal vitamin D, but fortified orange juice can be a source.


Like fruits, most vegetables are not significant sources of vitamin D, but fortified products like certain plant-based milks can provide it.


Vitamin D supplements are available for those who have limited sun exposure or dietary intake of Vitamin D.

What Is a Normal Range for Vitamin D?

The range for vitamin D levels, as measured in the blood, is typically expressed in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L). The optimal range for vitamin D is considered between 25 and 80 ng/mL. 

Ranges can vary slightly depending on the laboratory and the method used for testing, but generally, the accepted ranges are as follows:

  • Severe Deficiency: Less than 10ng/mL. This range could be associated with osteomalacia or rickets.

  • Mild Deficiency: Between 10 and 24 ng/mL. This level may be associated with secondary hyperparathyroidism and/or osteoporosis.

  • Optimal: Between 25 and 80 ng/mL. 

  • Possibly Toxic: Greater than 80 ng/mL. 

How Much Vitamin D Do I Need?

The Food and Drug Administration (FDA) recommends a daily allowance of 400 International Units (IU) of vitamin D. But some studies suggest that adults may need at least 800 IU to protect against bone fractures. 

However, these are general guidelines. The amount of vitamin D an individual needs through diet and sun exposure can vary based on several factors, including age, skin color, geographic location, and overall health. 

What Are the Symptoms of Low Vitamin D?

While many individuals with low vitamin D might not display clear symptoms, there are subtle signs that can indicate a potential shortfall. These can include:

  • Pain in bones

  • Joint discomfort (Arthralgias)

  • Muscle aches (Myalgias)

  • Tiredness

  • Twitching of muscles (fasciculations)

  • Lack of strength

Read More: 20 Best Vitamin D Supplements

What Causes Low Vitamin D?

Various physical and lifestyle elements can hinder the body's production and absorption of vitamin D. Several factors can limit sun exposure, reducing the amount of sunlight your skin receives. These factors can be environmental, personal or related to health and age:

  • Being homebound

  • Residing in polluted areas

  • Working night shifts

  • Having a darker skin complexion

  • Aging

What Prevents Vitamin D Absorption?

Additionally, certain conditions can interfere with the proper processing and absorption of vitamin D, leading to deficiencies. These include:

  • Conditions that obstruct the absorption of dietary fats (Celiac disease and Crohn’s disease)

  • Undergoing gastric bypass surgery

  • Having a higher body fat percentage

  • Higher caffeine intake

  • Liver diseases

Does Vitamin D Help the Immune System?

Vitamin D deficiency may lead to weakened immune function and increased susceptibility to infections.  Experts have sought to decode the link between vitamin D and immune health in recent years.

Now, a growing body of research hints at a potential relationship between long-term vitamin D deficiencies and the onset of autoimmune conditions like diabetes and rheumatoid arthritis. Yet, more research is needed to confirm these links. 

What Are the Different Types of Vitamin D?

Taking vitamin D supplements, when directed by a healthcare professional, may be a good option for addressing deficiency or insufficiency to avoid serious health problems. There are two main types of vitamin D: vitamin D2 and vitamin D3.

Vitamin D2

Vitamin D2 (Ergocalciferol) is derived from plant sources and is often used in prescription supplements. It can also be found in fortified foods. While vitamin D2 can raise blood levels of vitamin D, it is generally considered less effective at maintaining adequate levels compared to vitamin D3.

Vitamin D3

Vitamin D3 (Cholecalciferol) is naturally synthesized in the skin when exposed to sunlight. It is also available as a supplement and is typically more effective at raising and maintaining blood levels of vitamin D. Vitamin D3 supplements are widely available over-the-counter and are often preferred.

What Is the Difference Between Vitamin D2 and Vitamin D3?

Vitamin D2 is primarily obtained from plant sources and fortified foods, whereas Vitamin D3 comes from animal sources and is also produced by the skin in response to sunlight exposure. 

Both vitamin D2 and vitamin D3 can be used to correct deficiencies when prescribed by a healthcare provider. However, vitamin D3 is generally preferred for supplementation due to its greater efficacy in maintaining adequate vitamin D levels.

Be sure to consult with your healthcare provider to find out which vitamin D supplement to use.

Read More: What’s the Difference Between Vitamin D, D2, and D3?

Should You Take Vitamin D2 or D3?

When deciding whether to take vitamin D2 or vitamin D3, your healthcare professional should consider your dietary habits and health needs. 

Dietary Habits

Your choice might also depend on dietary preferences. Vitamin D3 is usually derived from animal sources (like fish oil or lanolin from sheep's wool), making it suitable for non-vegetarians. On the other hand, vitamin D2 is derived from plant sources and is often used in fortified foods and supplements, making it a good option for vegetarians and vegans.

Individual Health Needs

If you have a specific health condition, a deficiency, or unique dietary requirements, your healthcare provider might recommend one form over the other. For instance, individuals with certain allergies or dietary restrictions might prefer one type of supplement over the other.

Can You Take Too Much Vitamin D?

While rare, consuming excessive amounts of vitamin D can pose health risks. Excessive vitamin D intake from supplements can lead to calcium buildup in the blood.

This condition can trigger a range of unpleasant symptoms, including nausea, vomiting, weakness and frequent urination. Experts note that reaching hazardous levels is generally difficult despite these potential side effects. Symptoms of vitamin D toxicity are most likely to occur with a daily intake of at least 10,000 IU (250 mcg), according to the Institute of Medicine. Your body naturally regulates vitamin D, eliminating excess amounts to maintain balance.

The importance of the sunshine vitamin is undeniable, impacting our bones and maybe even our immune systems. Ensuring you get enough, whether through sun exposure, diet or supplements, is essential while still being cautious of not overdoing it.

Frequently Asked Questions About Vitamin D

What Vitamin Is Good for Bones?

Vitamin D and calcium are crucial for bone health. Vitamin D helps the body absorb calcium, which is a primary component of bone. Adequate levels of both nutrients are essential to maintain strong bones and prevent conditions like osteoporosis.

Does Vitamin D Give You Energy?

While vitamin D itself doesn't provide energy in the same way calories do, maintaining adequate vitamin D levels can support overall health, which may contribute to better energy levels. A deficiency in vitamin D can lead to fatigue and tiredness, so ensuring sufficient intake might help in feeling more energetic.

Is Vitamin D a Hormone?

Yes, vitamin D functions as a hormone in the body. It is produced by the skin in response to sunlight and then activated by the liver and kidneys. It plays a role in calcium absorption and bone health, among other physiological processes.

Can Vitamin D Deficiency Cause Hair Loss?

Vitamin D deficiency may be linked to hair loss, particularly in a condition known as alopecia areata. Adequate vitamin D levels are important for hair follicle cycling and health, so a deficiency might contribute to hair loss issues.

What Fruits Have Vitamin D?

Fruits generally contain very little to no vitamin D. The primary natural sources of vitamin D are fatty fish, liver, egg yolks, and fortified foods. For significant vitamin D intake, one should rely on these sources, supplements, or adequate sun exposure.

Does Low Vitamin D Make You Tired?

Yes, low levels of vitamin D can contribute to feelings of fatigue and tiredness. Vitamin D deficiency has been linked to a general sense of malaise and decreased energy levels, so maintaining sufficient vitamin D levels is important for overall energy and well-being.

Does Vitamin D Help with Weight Loss?

There is no conclusive evidence that vitamin D directly contributes to weight loss. However, maintaining adequate vitamin D levels can support overall health, which might indirectly assist with weight management. A balanced diet and regular exercise are more directly effective in weight loss efforts.

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high quality sources for our articles, and our editors review for accuracy, and trustworthiness. Review the sources used below for this article:

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