The Vitamin D3 Playbook: Benefits, Dosage, Deficiency, and More

Vitamin D is unique because it’s the only vitamin that can be produced by the skin when exposed to sunlight.

It’s a fat-soluble vitamin (meaning that it doesn’t dissolve in water—only in fats and oils) that also acts as a steroid hormone. Steroid hormones play an essential role in regulating metabolism, stress, inflammation, immune functions, salt and water balance, and the development of sexual traits and reproduction (1, 2).

With that being said, vitamin D influences your bones, intestines, immune and cardiovascular systems, pancreas, muscles, brain, calcium homeostasis, and the control of cell cycles (3, 4).

Because there are two different types of vitamin D in the human body (D2 and D3), both are simply called “vitamin D”.

Besides D2 and D3’s slightly different molecular structure, where they’re sourced from may be their biggest difference (3)...

• Vitamin D2 is naturally found in yeast and sun-exposed mushrooms.
• Vitamin D3 is naturally found in oily fish (like salmon, mackerel, and herring) and is produced by the skin when exposed to sunlight.

If you’re wondering which supplement to opt for—D2 or D3—current research is revealing that vitamin D3 supplements may be the better choice, especially if you’re wanting to raise your body’s vitamin D levels (5, 6).

Vitamin D receptors are present in most tissues and cells throughout the human body, but vitamin D2 and D3 need to undergo quite the process in order to get to those receptors...

Here’s what needs to happen: Vitamin D has to first be processed in the liver and kidneys. From there, specific proteins are needed to activate vitamin D2 and/or D3. Once activated, vitamin D can finally attach itself to the cells in your body and, in turn, stimulate the absorption of the calcium and phosphate you get from food (3).

Without vitamin D, only 10 to 15% of calcium and 60% of phosphorus are absorbed. With vitamin D, those percentages jump to 30% to 40% for calcium and 80% for phosphorus (4).

Why is this so important?

Because calcium is fundamental for strong bones while phosphate is critical for healthy bones, teeth, muscles, nerves, and basic bodily functions (7).

Without this fat-soluble vitamin, your body wouldn’t be able to absorb calcium, magnesium, or phosphate. Which would inhibit the maintenance of your health, bones, immunity, and more.

Vitamin D3 has many uses, including prevention of the following:

• Bone disorders (think: rickets, osteomalacia, and osteoporosis)
• Cancer (up to 77% reduced risk)
• Heart disease
• MS
• Autism
• Mental illness
• ADHD
• Asthma
• COVID-19 (but only if the dose is correct) (8)

Vitamin D deficiency can be caused by a variety of factors—and can lead to a whole host of problems.

Problems due to vitamin D deficiency escalated in the early-to-mid 1900s—with rickets (a vitamin D deficiency among infants and children that softened bones) skyrocketing across the globe.

To solve this problem, manufacturers began fortifying milk with vitamin D in 1930, which effectively ended rickets (4). Now you can find fortified cereals, granola bars, and yogurts lining grocery store shelves, too.

However, 35% of Americans are still deficient in this essential vitamin, with an estimated 1 billion being affected worldwide.

Which leads us to the following question: Why?

For one, malabsorption conditions like celiac disease and inflammatory bowel disease can lead to a vitamin D deficiency. This is because the small intestine can’t absorb enough nutrients and fluids, which means that vitamin D can’t be utilized by the body (9).

Secondly, those in nursing homes and hospitals—along with those who wear full-body coverings for cultural and religious reasons—aren’t getting adequate amounts of sun exposure.

Taking these two points into consideration—along with the fact that vitamin D is found in very few foods—shows just how essential it is to consume a vitamin D supplement.

Conditions Linked to a Vitamin D Deficiency

• Cancer
• Cardiovascular disease
• Diabetes
• Autoimmune diseases
• Depression
• Chronic liver disease

Medications like phenobarbital, carbamazepine, dexamethasone, nifedipine, spironolactone, clotrimazole, and rifampin can also play a role in vitamin D deficiency.

When sunlight hits the skin, a chain of reactions occurs, prompting the body to produce vitamin D—approximately 50 to 90% of your daily needs, in fact. Experts recommend 20 minutes of sunshine daily, with 40% of your skin exposed (4).

So, yes, the human body is able to produce vitamin D with the right amount of sun exposure, but more often than not, sunlight isn’t enough to meet your daily requirements. Especially when you take into consideration things like skin pigmentation, weather, and time of day.

This is where a vitamin D3 supplement comes into play.

According to the National Institutes of Health (NIH), the Recommended Dietary Allowances (RDAs) are the following (10):

• 0 to 12 months — 10 mcg (400 IU)
• 1 to 13 years — 15 mcg (600 IU)
• 14 to 18 years — 15 mcg (600 IU)
• 19 to 50 years — 15 mcg (600 IU)
• 51 to 70 years — 15 mcg (600 IU)
• 70+ years — 20 mcg (800 IU)

*IU = International Units

How Long Does It Take Vitamin D3 to Work?

Depending on how deficient you are, it could take 2 to 3 months to get your vitamin D levels where they need to be.

Even with the guidelines from the National Institutes of Health, there has yet to be an international agreement on vitamin D intake.

The Endocrine Society recommends 1,500 to 2,000 IU daily for adults, while the United Kingdom advises just 400 IU per day for those four or older (11, 12).

To determine your unique vitamin D dosage, consult your doctor. Again, the dosage can depend on your current state of health, skin pigmentation, and weather.

Is It Possible to Take Too Much Vitamin D3?

Although extremely rare, vitamin D toxicity can occur at extremely high doses. The reported doses of vitamin D toxicity actually happening range from 50,000 IU to 1,604,000 IU per day (13).

This toxicity results in a buildup of calcium in your blood (hypercalcemia), causing nausea, vomiting, weakness, and frequent urination. It may also lead to bone pain and kidney problems, like the formation of calcium stones (14, 13).

When it comes to vitamin D3 and other medications and supplements, there are a few things to keep in mind…

Registered Dietitian, Janet Coleman, explains, “Many people are confused about whether or not vitamin D3 can be taken with other supplements. The answer is, it depends. Vitamin D3 is fat-soluble, which means that it can react negatively to other fat-soluble vitamins, like vitamin A and E.”

Coleman continues, “It also depends on what else you’re taking. For instance, if you’re taking calcium supplements, it’s recommended to pause your vitamin D3 supplementation for a time since vitamin D3 and calcium compete for absorption in the body.”

Medications & Vitamins That Hinder Vitamin D3 Absorption

• Aluminum
• Anti-hypertensive Drugs and Calcium Channel Blockers (like Diltiazem and Cardizem)
• Blood Pressure Medication (like Verapamil and Calan)
• Calcipotriene: Another form of vitamin D used to treat plaque psoriasis
• Cholesterol Medication (like Atorvastatin and Lipitor)
• Heart Failure and Irregular Heartbeat Medication (like Digoxin and Lanoxin)
• Steroids (like Prednisone)
• Vitamin A
• Vitamin E
• Water Pills
• Weight Loss Pills (like Orlistat, Xenical, and Alli)

To sum it up, “It was found that vitamin D3 does work well with most other supplements, but studies have shown that this varies based on the individual. Some people experienced side effects while taking dietary supplements in combination with vitamin D3, while others did not.”

“The key is to consult with your doctor before starting any new supplement regimen. It’s crucial to discuss your health history and current medications as well as the ingredients of any supplements you consume.”

NativeTip: When supplementing with vitamin D3, it’s recommended to take it two hours before or after taking other medications.

Because vitamin D3 is a fat-soluble vitamin, you’ll want to take it with high-fat foods. By pairing it with a meal, it will be better absorbed into your bloodstream.

In one 2010 study, 17 individuals with a vitamin D deficiency were instructed to take their usual vitamin D supplement with the largest meal of the day. After just 3 months, results showed a 50% increase in the serum levels of vitamin D (15).

Another study, conducted in 2014, examined the absorption of vitamin D3 when taken with a high-fat meal versus that of a fat-free meal. This one-day study was completed by 50 healthy old men and women. The results were apparent in just 12 hours—with vitamin D3 levels increasing by 32% among those who ate a high-fat meal (16).

Now that you’re an expert on vitamin D3, let’s discuss which supplement is best, and why.

Vitamin D3 supplements are found in the following forms:

• Softgel capsules
• Gummies
• Powder
• Oil droppers

Although future research is still needed to determine which form of vitamin D is best, one 2011 study found that oil-based vitamin D produced a greater increase in the serum levels of individuals compared to that of powder and ethanol-based vitamin D (17).

In addition to the form of vitamin D3, there is one essential vitamin that, when combined with vitamin D3, significantly increases bone mineral density (BMD) while decreasing glucose levels (18, 19).

That vitamin, you ask?

Vitamin K2.

In addition to the benefits listed above, it also helps “shuttle calcium from your blood to your bones”, says Dr. Victoria Glass of the Farr Institute. This, in turn, helps fight off osteoporosis while simultaneously preventing the calcification and stiffening of arteries. This is exceptional news, especially for older adults and postmenopausal women (20).

With that being said, it’s essential that your vitamin D3 supplement have vitamin K2. They are proven to benefit both bone and cardiovascular health (21, 22).