Vitamin D: Bridging the Gap Between Sunlight and Supplements

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Vitamin D is crucial for good health, but a surprising 41.6% of people don’t get enough of it. The numbers are even more alarming among specific groups: 82.1% of black individuals and 69.2% of Hispanics are vitamin D deficient. [PMID: 21310306] In this article, we’ll explore the benefits of vitamin D supplements and why they’re an essential tool for improving health, particularly for those who are most at risk.

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin that is essential for bone health, immune function, and other important physiological processes in the body. It is sometimes called the “sunshine vitamin” because the body can produce it when the skin is exposed to sunlight. There are two main forms of Vitamin D: Vitamin D2 (ergocalciferol), found in some plant-based foods, such as mushrooms that have been exposed to ultraviolet light, and Vitamin D3 (cholecalciferol), produced by the body when the skin is exposed to sunlight and found in some animal-based foods, such as fatty fish and egg yolks.

Vitamin D plays a critical role in regulating the absorption and utilization of calcium and phosphorus, which are essential for bone health. It also helps to regulate immune function and may have other important roles in the body, including in the nervous system and cardiovascular system.

What Are The Benefits of Vitamin D?

Vitamin D is essential for various functions in the body, and has several potential health benefits. Here are some of the health benefits of Vitamin D:

  • Lower All Cause Mortality: Researchers found, “This study confirmed an inverse association between serum 25(OH)D concentrations and age-adjusted all-cause mortality rates. Overall, individuals whose 25(OH)D concentrations were in the lowest quantile (0–9 ng/mL) had nearly twice the age-adjusted death rate as those in the highest quantile (> 35 ng/mL).” [PMC4103214]
  • Bone health – Vitamin D plays a key role in regulating the absorption and utilization of calcium and phosphorus, which are essential for bone health. Adequate Vitamin D intake may help to prevent bone fractures and osteoporosis. [PMC3257679] [PMID: 21872800]
  • Immune function – Vitamin D helps to regulate immune function and may help to reduce the risk of infectious diseases such as the flu, colds, and tuberculosis. [PMC9456003] [PMC7551809]
  • Autoimmune Diseases: The role of vitamin D has been studied in the control of several autoimmune conditions such as inflammatory bowel disease (IBD), celiac disease, type 1 diabetes mellitus, and others. [PMID: 36336872]
  • Mood regulation – Serum vitamin D levels inversely correlate with clinical depression. Vitamin D may play a role in regulating mood and reducing the risk of depression. [PMC6970300] It plays a role in serotonin production, which can lift mood and may help alleviate symptoms of depression [PMID: 23377209] and anxiety. [PMC6390422]
    • Anxiety and Stress: Researchers studying generalized anxiety disorder (GAD) found that Vitamin D supplementation was effective in reducing anxiety severity by increasing serotonin and decreasing an inflammatory biomarker, neopterin, in GAD patients. [PMID: 31478182]
  • Heart health – Vitamin D may help to reduce the risk of heart disease by regulating blood pressure, reducing inflammation, and improving insulin sensitivity. [PMC8968037] [PMID: 33234810]
  • Pain: In a review of the studies on Vitamin D and pain, researchers concluded that vitamin D supplementation could have a role in the management of chronic pain. [PMID: 27676659]
  • Fatigue: Researchers found that Vitamin D treatment improved fatigue in otherwise healthy people with vitamin D deficiency. [PMC5207540]
  • Diabetes Prevention: Vitamin D supplementation helps to improve insulin sensitivity in people with low Vitamin D status. [PMC8684490] Some research indicates that sufficient levels of this nutrient can lower the risk of developing type 2 diabetes.
  • Brain Health: Vitamin D may contribute to brain health and function. Two large prospective studies recently indicated that low vitamin D concentrations may increase the risk of cognitive decline. [PMID: 22536767]
  • Cancer Prevention: Vitamin D may play a role in reducing the risk of certain cancers, such as colon, breast, and prostate cancers. [PMC1470481] [PMC5938036]

Over a billion people worldwide are Vitamin D deficient or insufficient.

Vitamin D Deficiency- An Ignored Epidemic

Vitamin D Status And Covid Rates

Although the Covid emergency may be over, the virus continues to cause disease and disability. Adequate Vitamin D levels can cut the risk of illness.

A study looked at whether having enough Vitamin D in your system has any link with catching COVID-19. They checked Vitamin D levels and COVID-19 test results of over 190,000 people from all over the U.S. They found that people with low Vitamin D levels were more likely to test positive for COVID-19 compared to those with adequate or high levels of Vitamin D. This was true for people of different ages, genders, and ethnicities, and in different parts of the country. The study suggests that having good Vitamin D levels might be helpful in lowering the risk of getting COVID-19.

The overall prevalence rate of vitamin D deficiency was 41.6%, with the highest rate seen in blacks (82.1%), followed by Hispanics (69.2%).

Prevalence and correlates of vitamin D deficiency in US adults

Vitamin D Deficiency: How Common Is It?

Vitamin D deficiency is surprisingly common in North America, affecting upwards of 40% of the U.S. population alone. This deficiency is more prevalent in northern regions, where sunlight exposure is limited, especially during the winter months. Factors such as spending a lot of time indoors, wearing clothing that covers most of the skin, and having darker skin can reduce the body’s ability to produce Vitamin D from sunlight.

Surprisingly, anyone living north of Atlanta may have difficulty making enough Vitamin D through sunlight exposure during winter months. This relates to the angle of the sun and shorter daylight hours in these northern latitudes. The skin’s ability to produce enough Vitamin D is especially decreased during the fall and winter months.

Here are the risk factors for Vitamin D deficiency:

  • People living in northern latitudes
  • Elderly people
  • People with darker skin tones
  • People digestive problems, like Crohn’s or celiac disease
  • People who have had baria
  • Indoor workers
  • Those who frequently use sunscreen
  • People with a BMI over 30, clinically defined as obesity.
  • Infants who are exclusively breastfed
  • Pregnant and breastfeeding women
  • People taking certain medications, like anticonvulsants and corticosteroids
  • People who have had Roux-en-Y gastric bypass or sleeve gastrectomy
  • People who have had their gallbladders removed

Anyone with risk factors for deficiency would want to have their Vitamin D tested to find out what their Vitamin D levels are at baseline and/or after a period of Vitamin D supplementation.

Vitamin D Deficiency, Secondary Hyperparathyroidism, and Bone Loss

Vitamin D plays a pivotal role in maintaining our body’s calcium balance, a key factor in bone health. When Vitamin D levels are low, the body’s ability to absorb calcium from food diminishes. Low levels of calcium in the blood (hypocalcemia) can trigger the parathyroid glands to start producing more parathyroid hormone (PTH) in an attempt to maintain calcium equilibrium. This condition, known as secondary hyperparathyroidism, results in the body extracting more calcium from the bones to compensate low blood calcium. Over time, this process can lead to bone loss and an increased risk of osteoporosis, a condition characterized by porous and fragile bones.

The use of Vitamin D supplements is a key strategy in preventing this cascade of events. By ensuring adequate Vitamin D levels, calcium absorption in the intestines is optimized, reducing the need for the parathyroid glands to release excess PTH. This not only helps in maintaining a healthy calcium balance but also prevents the excessive leaching of calcium from bones, thereby protecting bone density and strength.

The following groups of drugs were identified in one or more studies to affect vitamin D status in some way: anti-epileptics, laxatives, metformin, loop diuretics, angiotensin-converting enzyme inhibitors, thiazide diuretics, statins, calcium channel blockers, antagonists of vitamin K, platelet aggregation inhibitors, digoxin, potassium-sparing diuretics, benzodiazepines, antidepressants, proton pump inhibitors, histamine H2-receptor antagonists, bile acid sequestrants, corticosteroids, antimicrobials, sulphonamides and urea derivatives, lipase inhibitors, hydroxychloroquine, highly active antiretroviral agents, and certain chemotherapeutic agents. 

A Literature Review of the Potential Impact of Medication on Vitamin D Status [PMC8373308]

The Importance of Testing Your Vitamin D

Vitamin D testing is vital for determining the appropriate dosage of vitamin D supplementation. While vitamin D is crucial for healthy bones, immune function, and many other bodily processes, too much or too little can have adverse effects.

If your body has insufficient vitamin D, you may be at risk for bone diseases like osteoporosis. On the other hand, an excess of vitamin D can lead to high blood calcium potentially causing kidney stones and heart problems. Vitamin D levels can vary based on factors like sun exposure, diet, and certain medical conditions. A simple blood test can measure your current vitamin D levels, enabling your healthcare provider to prescribe a precise supplementation dose to optimize your health while minimizing the risk of adverse effects. This makes vitamin D testing a crucial step in establishing the proper dose for vitamin D. Vitamin D dosages should be adjusted based on your blood level with many clinicians recommending an optimal Vitamin D level of 50-80 ng/ml. Vitamin D Labs (affiliate link) can be ordered in the NutriScape Lab Shop.

There is some controversy over what should be considered a good level of Vitamin D. The normal range for Vitamin D goes down to 20 ng/ml, but many clinicians believe the optimal range is 45-60 ng/ml.

If you’re diagnosed with a deficiency, your doctor might prescribe a high-dose of vitamin D2, often 50,000 IU per week for about eight weeks. After that, a maintenance dose of 800 to 1,000 IU of vitamin D3 daily is commonly recommended. [PMID: 19835345]

Dosing Vitamin D Supplements to Increase Blood Levels

The amount of vitamin D supplementation needed to increase blood levels can vary widely from one person to the next due to factors such as body weight, baseline vitamin D levels, age, skin color, sun exposure, and individual response to vitamin D intake.

On average, it’s often cited that each additional 1,000 IU of vitamin D3 could raise blood levels by about 10 ng/ml (nanograms per milliliter) over a period of several months. However, this is a rough estimate and individual responses can differ. Some people may experience greater increases, while others less.

To determine the exact impact of vitamin D supplementation on an individual’s serum 25(OH)D levels, blood tests before and after supplementation are the most accurate method. If someone is considering vitamin D supplementation or adjusting their current dose, it’s best done under the guidance of a healthcare professional who is checking your labs.

Vitamin D Softgel vs. Powder Capsule

Vitamin D supplements come in different forms, including softgels and dry capsules. The bioavailability of vitamin D supplements can vary between these forms. Softgels contain vitamin D dissolved in an oil, which aligns with the fat-soluble nature of vitamin D, potentially enhancing its absorption in the digestive tract. This is because fat-soluble vitamins are absorbed alongside dietary fats, and the presence of oil within the softgel may be better absorbed. On the other hand, dry capsules often contain vitamin D in a powdered form, which may not be absorbed as efficiently as the oil-based form, especially if taken without dietary fat. However, the actual difference in bioavailability between these two forms may be small for individuals with normal digestion, and both can effectively increase vitamin D levels when taken correctly. Ultimately, the best form of vitamin D supplement can depend on individual needs, preferences, and any specific digestive or health concerns.

What Happens If You Take Too Much Vitamin D?

The primary concern with too much Vitamin D is elevated levels of calcium in the blood. This excess Vitamin D increases the body’s calcium absorption, leading to a range of health issues. High levels of calcium in the kidneys can result in kidney stones, causing severe pain and kidney dysfunction. Elevated blood calcium levels can also lead to calcification in tissues and organs, such as the heart and kidneys, which impairs their function.

Vitamin K2 may help reduce this risk. Vitamin K2 helps direct calcium to the bones and teeth where it’s needed, rather than allowing it to accumulate in soft tissues, thereby reducing the risk of calcification in organs like the heart and kidneys.

Ironically, an overdose of Vitamin D can even weaken bones. While calcium is essential for strong bones, Vitamin D can cause elevated levels of calcium in the blood which can trigger a response where the body starts to pull calcium away from the bones and deposit it into the bloodstream. This process is called bone resorption, and it can weaken the bone structure over time.

What’s The Difference Between D2 and D3?

Vitamin D2 and D3 both help keep our bones and immune system strong, but they aren’t the same. D3 is the more active version in the body. It’s better at quickly and efficiently raising our vitamin D levels because the body metabolizes, or processes, it differently. Specifically, it converts D3 into calcitriol, its active form, at a faster rate than D2. This leads to a more stable and long-lasting increase in Vitamin D in our bodies. Therefore, if you’re looking to boost your Vitamin D levels through a supplement, choosing D3 is better.

What is The RDA For Vitamin D?

Here’s a table outlining the Recommended Dietary Allowance (RDA) for Vitamin D for different age groups:

Age GroupRDA for Vitamin D (IU)
0-12 months400
1-18 years600
19-50 years600
51-70 years600
71 years and up800
Pregnant Women600
Breastfeeding Women600

Why The RDA Might Not Be Enough

Vitamin D deficiency is a concern that disproportionately affects certain risk groups and individuals residing in northern latitudes. For instance, older adults have skin that is less efficient in synthesizing Vitamin D from sunlight, and they may also spend more time indoors, away from natural light sources. People with darker skin tones have higher levels of melanin, which reduces the skin’s ability to produce Vitamin D from sunlight. Additionally, those who live in northern regions experience fewer hours of sunlight, especially during the winter months, making the natural synthesis of Vitamin D challenging.

Even those who are outdoors frequently might not get enough due to the angle of the sun and the need to wear more clothing. While the Recommended Dietary Allowance (RDA) serves as a general guideline for Vitamin D intake, it might not fully address the needs of these specific populations. Therefore, getting tested for Vitamin D levels becomes increasingly important for people within these risk groups. This targeted approach allows for more personalized supplementation plans to help meet individual health needs.

Food Sources of Vitamin D.

Here’s a table listing some common food sources of vitamin D and the approximate amount of vitamin D they contain. Please note that these values are approximate and can vary depending on factors like cooking methods, serving sizes, and food sources.

Food SourceAmount of Vitamin D (IU) per serving
Cod liver oil (1 tablespoon)1360
Salmon, cooked (3 ounces)450 – 1000
Mackerel, cooked (3 ounces)345
Tuna, canned in water (3 ounces)154
Sardines, canned in oil (2 sardines)46
Beef liver, cooked (3 ounces)42
Egg yolk (1 large)41
Fortified milk or Juice (8 ounces)100 – 120
Fortified yogurt (6 ounces)80 – 100
Fortified cereal (1 serving)40 – 100
IU stands for International Units.

Are Vitamin D Supplements Safe?

Vitamin D supplements are generally safe for most people when taken within recommended limits. Overdosing is rare but could lead to problems like high calcium levels in the blood. For those who are deficient, taking a supplement can be an effective way to reach optimal levels. It’s important to choose the dosage recommended by a healthcare provider that will keep your Vitamin D levels in the optimal range. Vitamin K2 can help regulate calcium levels in the body, potentially reducing the risk of hypercalcemia caused by Vitamin D supplementation. So, taking Vitamin D supplements that also include Vitamin K2 might offer a safer option

Medication Interactions With Vitamin D

  • Anticonvulsants: These medications can lower vitamin D levels, potentially reducing its effectiveness and increasing the risk of deficiency. Examples: Phenytoin, carbamazepine, phenobarbital.
  • Corticosteroids: Long-term use of corticosteroids can reduce calcium absorption and impair vitamin D metabolism, potentially leading to bone loss. Examples: Prednisone, hydrocortisone, dexamethasone
  • Calcium channel blockers: High levels of vitamin D can increase calcium levels in the blood, potentially reducing the effectiveness of calcium channel blockers. Examples: Amlodipine, nifedipine, diltiazem.
  • Orlistat: Orlistat can reduce the absorption of fat-soluble vitamins, including vitamin D, potentially leading to deficiency. Examples: Xenical, Alli (over-the-counter).
  • Cholestyramine and Colestipol: These medications can reduce the absorption of fat-soluble vitamins, including vitamin D, potentially leading to deficiency. Examples: Questran, Colestid.
  • Calcipotriene: Using high doses of vitamin D supplements in combination with calcipotriene may cause elevated levels of calcium in the blood, potentially leading to serious health complications. Example: Dovonex (topical psoriasis medication).
  • Digoxin: High levels of vitamin D can increase calcium levels, which may increase the risk of side effects and toxicity from digoxin. Example: Lanoxin.
  • Thiazide diuretics: These medications can increase calcium levels in the blood, and high doses of vitamin D may exacerbate this effect, potentially leading to hypercalcemia. Examples: Hydrochlorothiazide, chlorthalidone.

The following groups of drugs were identified in one or more studies to affect vitamin D status in some way: anti-epileptics, laxatives, metformin, loop diuretics, angiotensin-converting enzyme inhibitors, thiazide diuretics, statins, calcium channel blockers, antagonists of vitamin K, platelet aggregation inhibitors, digoxin, potassium-sparing diuretics, benzodiazepines, antidepressants, proton pump inhibitors, histamine H2-receptor antagonists, bile acid sequestrants, corticosteroids, antimicrobials, sulphonamides and urea derivatives, lipase inhibitors, hydroxychloroquine, highly active antiretroviral agents, and certain chemotherapeutic agents. 

A Literature Review of the Potential Impact of Medication on Vitamin D Status [PMC8373308]

Supplement Interactions with Vitamin D

  • Calcium: High levels of vitamin D can increase calcium absorption, potentially leading to hypercalcemia (elevated blood calcium levels) if calcium supplements are also taken in high doses.
  • Magnesium: Magnesium is involved in the conversion of vitamin D to its active form, and adequate magnesium levels may help optimize vitamin D status. However, excessively high magnesium intake could lead to hypermagnesemia, which can interfere with vitamin D metabolism.
  • Phosphorus: Both vitamin D and phosphorus play crucial roles in bone health, and their levels need to be balanced. High levels of vitamin D can increase phosphorus absorption, potentially causing an imbalance if phosphorus supplements are also taken in high doses.
  • Vitamin A: Excessive intake of vitamin A can interfere with vitamin D’s ability to maintain healthy calcium levels. However, the interaction between vitamin A and vitamin D is complex, and further research is needed to fully understand their relationship.
  • Vitamin K: Both vitamin D and vitamin K are involved in bone health and calcium regulation. It’s important to maintain a balance between these vitamins to avoid potential negative effects on bone health and blood clotting.

Vitamin D / K2 / Calcium Relationships

There is a concern that if a person takes too much Vitamin D and/or Calcium supplements, causing high calcium levels in the blood. This excess calcium may end up in the arteries and specifically in the arteries of the heart and carotid arteries where it can cause cardiovascular disease.

This is where Vitamin K2 comes into the picture. Vitamin K2 plays a role in regulating where calcium ends up in the body. It’s involved in activating proteins that help keep calcium in bones and teeth and out of arteries and other soft tissues. Therefore, it’s thought that getting enough vitamin K2 will help prevent calcium from accumulating in the arteries.

Essentially, getting enough Vitamin K2 along with Vitamin D and Calcium causes calcium to go to the bones where it’s needed, rather than into the artery walls where it can cause real problems. The relationships between vitamin D, calcium, and vitamin K2 in the body, and their effects on health, are complex and not fully understood.

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Vitamin D (5000IU) K2 (100 mcg)

Adjust your dose to achieve a Lab Value of greater than 45 ng/ml, which many clinicians consider to be the optimal range for Vitamin D.

Vitamins D3 and K2 have been extensively studied regarding their roles in calcium metabolism.* Research indicates that a synergistic relationship exists between vitamin K2 and vitamin D3, especially in terms of bone strength and cardiovascular health.* While vitamin D3 is recognized for its role in calcium absorption and metabolism, it is vitamin K2 that directs calcium to bones rather than joint spaces and arteries.* This product is formulated with a clinically relevant dose of MK-7, a unique, soy-free form of vitamin K2 that has been shown to promote healthy vascular structures.*

Amount Per 1 Capsule Serving
Vitamin D3 … 125mcg (5, 000IU) (as Cholecalciferol) (from Lanolin)
Vitamin K2 … 180mcg (as Menaquinone-7) (MK-7) (MenaQ7®)

Note: Vitamin K may interact with medications for blood-thinning. Consult a healthcare professional prior to use if you take this type of medication.


Vitamin D3 5000 IU by Nordic Naturals

Vitamin D3 5000 is Nordic Naturals’ signature high-potency vitamin D product, suitable for clinical applications aimed to correct or avoid vitamin D deficiency, or to fast-track support for overall health and wellness.* With 5000 I.U. of natural vitamin D3 (cholecalciferol) in extra virgin olive oil, Vitamin D3 5000 helps replenish vitamin D in tissue stores, supporting patients at increased risk of deficiency.*

This product does not contain fish oil. Take as directed by a healthcare practitioner.

Amount Per 1 Soft Gel Serving
Vitamin D3
 … 5000IU (Cholecalciferol)


Food First!

Although this article discusses supplements in detail, don’t forget that we are absolutely committed to the “Food First” approach to nutrition. When it comes to your health, the totality of your eating habits far surpasses the impact of individual nutrients or any single supplement you consume. Even though this article doesn’t delve into the broader picture of your overall diet, it’s crucial to keep this element at the forefront of our minds. Your food needs to provide all the vitamins, minerals, fiber, and phytochemicals to nourish your body systems down to the cellular level.

Food choices, rather than supplements, are the most critical factors for a healthy gut microbiome. These trillions of tiny inhabitants in your gut affect your brain waves; they orchestrate your immune system. They possess the power to create molecules that can switch genes on or off and are even capable of synthesizing neurotransmitters. Opting for organic foods and steering clear of plastic packaging (including those labeled BPA-free) is a smart move to limit toxin exposure. The sum of all these parts leads to a powerful conclusion: the ultimate key to your health lies in the quality and balance of the food you consume. Supplements are secondary.

To Sum It Up

Vitamin D, often referred to as the ‘sunshine vitamin’, plays a vital role in our overall health. It supports optimal bone health, boosts immune function, and potentially aids in the prevention of numerous chronic conditions. Despite the human body’s ability to generate this nutrient naturally through sun exposure, many people are not obtaining the necessary levels, often due to lifestyle or geographical factors. Incorporating more Vitamin D rich foods into your diet, considering supplements, and getting more sunlight are practical measures to ensure sufficient intake.


This Article is Not a Substitute for Medical Advice

Dietary supplements are not designed to diagnose, treat, cure, or prevent any disease. The Supplement Sciences website seeks to provide comprehensive access to the most relevant supplement information along with convenient online ordering. We do not provide medical advice and cannot guarantee that every product suggested is completely without risk. Since each person is unique in their health history and medication use, it is important to discuss supplements with your personal physician. Specifically, pregnant women and individuals being treated for cancer or liver or kidney problems must consult their physician about every nutritional supplement they plan to take. People taking medications for the treatment of HIV or with a history of organ transplant must not take supplements without consulting with their physician.


About the Author

Stephanie Figon, MS, RDN, LD

Creator of Supplement Sciences and NutriScape.NET. As a dietitian since 1992, Steph has had experiences in consulting, 15 years in clinical, and has operated a private practice nutrition counseling office for since 2011. Log in to comment and save this article on your board or send your comments to reviews@supplement-sciences.com

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