Vitamin D

What is the Big Deal About Vitamin D?

Vitamin D supports many functions of your body - you don't want it too high, but when it's too low, plenty of things can go wrong. 

Vitamin D supports many of our biological functions—including calcium absorption, bone health, muscle strength and coordination, immune regulation, cardiac function, blood pressure, neurotransmitter synthesis, mood and cognition, as well as many other things. 

   

Vitamin D comes in two major forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol):

• Vitamin D2 is derived from plant sources and fortified foods.

• Vitamin D3 is produced in the skin when it's exposed to ultraviolet B (UVB) rays from sunlight. Unlike most vitamins, the human body can actually synthesize vitamin D3 naturally through sun exposure.  

• Both D2 and D3 can also be manufactured synthetically in laboratories for use in supplements and fortified products

While both vitamin B2 and B3 both support many functions within the body, vitamin D3 is more effective at raising and maintaining blood levels of vitamin D. It remains in the body longer and produces higher levels of calcifediol, the circulating form of vitamin D.

Depending on the source, estimates of vitamin D deficiency in the United States range anywhere from 10% to 75%. Why such a wide gap? It comes down to how researchers define “low” vitamin D—a definition that’s still debated today.

In the early 2000s, researchers began to realize just how essential vitamin D is—not only for bone growth and maintenance (which was initially their primary focus), but also as a potential factor in diabetes, hypertension, metabolic syndrome, and ischemic heart disease. As a result, the threshold for what was considered “normal” vitamin D levels was raised. This shift meant that many more people were suddenly classified as deficient or insufficient.

With growing awareness of vitamin D’s impact on multiple body systems, healthcare providers began routinely ordering vitamin D blood tests for their patients. What followed was a surge of attention around vitamin D that was backed by evidence.

Today, the parameters for deficiency remain a topic of ongoing debate. But one thing is clear: vitamin D plays a vital role in health far beyond bones.

When healthcare providers began routinely testing vitamin D levels, they discovered that a surprising number of patients had low levels. Today, an ideal blood level is considered to be around 50 nmol/L (20 ng/mL), while anything below 30 nmol/L is generally viewed as inadequate.

Even though many foods are now fortified with vitamin D, and most people meet the recommended intake, blood levels still tend to hover at the lower end of normal. Why? Because oral intake is only part of the equation. A variety of other factors influence vitamin D status—including how well it’s absorbed, how efficiently it’s synthesized in the skin, and how it's processed by the liver and kidneys.

One of the most significant contributors to Vitamin D in our bodies is the sun: When the sun hits the skin, the body produces vitamin D. A lot of factors influence vitamin D absorption:

• Sedentary Behavior - Many people are sedentary these days (lots of computer work) and don't get out into the sun. When they do, they use sunblock to protect their skin from cancer-causing rays (an SPF of 8 or above reduces vitamin D absorption by 95%). 

• Skin Color - Air pollution also blocks the UVB rays that we need to synthesize vitamin D, so vitamin D levels are suffering in many people. People with darker skin absorb less vitamin D, so they tend to have lower blood levels of vitamin D. 

• Aging - Older adults are at greater risk of vitamin D deficiency due to reduced sun exposure and a natural decline in the skin’s ability to synthesize vitamin D from UV light.

• Geographical region - People living at higher latitudes (farther north) and altitudes tend to get less sunlight so are more likely to have lower vitamin D levels.

Interestingly, most organizations do not recommend that people get their vitamin D levels checked unless they have risk factors (for example, osteoporosis and certain vegan diets).

In this day and age of sedentary living (i.e., age of technology), sunscreens, air pollution, and vegan diets, everyone should get it checked at least once to establish a baseline every few years. Vitamin D testing Is especially important for the following individuals:

• Symptoms of low vitamin D (e.g. fatigue, bone pain, muscle weakness, mood changes)

• Bone disorders: osteoporosis, osteomalacia

• Chronic kidney or liver disease

• Alcoholism

• Malabsorption syndromes: celiac disease, Crohn’s disease, bowel surgery

• Dark skin or limited sun exposure

• Older age, especially with fall or fracture risk

• Immune or inflammatory conditions

• Diets that may limit vitamin D intake or absorption, including:
  Strict vegan or plant-based
  Low-fat or fat-free
  Gluten-free (especially for celiac)
  Low-FODMAP diets
  Elimination diets for IBS
  High-protein diets with limited fortified foods

• Family history of vitamin D deficiency/osteoporosis 

Benefits of Vitamin D

General: Antiviral, anti-inflammatory properties. Among other things, vitamin D plays a great role in regulating calcium, magnesium and phosphate absorption. All of these are essential in cell growth and functioning.

Respiratory: Vitamin D may help prevent colds, flu and other viral upper respiratory infections (including COVID-19 risk and symptoms); low vitamin D levels can potentiate allergies; Adequate levels of vitamin D tend to reduce risks of allergy problems as well as asthma and COPD exacerbation

Ears: Adequate blood levels may help with some cases of hearing loss.

Eyes: Vitamin D can help reduce the incidence and progression of macular degeneration

Gastrointestinal: May help inflammatory bowel disease and inflammatory intestinal disorders. Helps strengthen teeth and reduce the risk of periodontal disease. Adequate levels may reduce fatty liver disease.

Genitourinary: Sufficient levels may decrease overactive bladder. May help decrease symptoms of premenstrual syndrome (PMS) and polycystic ovarian syndrome (PCOS). May help with fibroids.

Cardiovascular: Helps to lower blood pressure and may help with heart disease; sufficient levels can lower your risk of a heart attack

Musculoskeletal: Overall, it helps increase calcium absorption. It may help with neuromuscular problems and decrease inflammation. Promotes bone growth and strengthens bones: helps prevent osteoporosis, may decrease fracture risk in those over 65 and may help prevent fractures in athletes; may reduce the pain of fibromyalgia, slow the progression of multiple sclerosis and adequate levels of vitamin D may help with rheumatoid arthritis. May help reduce chronic pain. It may also help with muscle weakness.

Skin: Psoriasis (topical). Helps stimulate collagen production. May lessen episodes of chronic urticaria. Eczema. May reduce acne.

Glucose: May help decrease insulin resistance and reduce the risk of diabetes

Immunity: Enhances immunity and may help prevent autoimmune diseases

Cancer: Adequate levels possibly help prevent the development and spread of certain cancers (especially breast, colon, bladder and prostate cancers)

Endocrine: Adequate levels of vitamin D may help assist in thyroid regulation

Neurologic: It may help to slow cognitive decline/enhance cognition in older people, Alzheimer's, dementia, and autism (a possibility per Vitamin D Council). Also, it may help with chronic fatigue. Vitamin D is also known to enhance brain function and may help enhance sleep. Sufficient levels can lower your risk for a stroke. It may help reduce muscle weakness. Chronic headaches. May improve balance. May decrease episodes of benign positional vertigo. May reduce lupus flares. 

Mental Health: Adequate - but not very high levels - high)  of Vitamin D may help reduce depression. Adequate levels of vitamin D may enhance the effects of serotonin reuptake inhibitors (SSRIs - taken for depression and anxiety). May help increase energy.

Infectious Disease: Possibly helps slow HIV progression

Other: May slow weight gain when taken in conjunction with calcium, and decreases generalized inflammation in the body. May enhance the activity of statin drugs (used to lower cholesterol)

Signs and Symptoms of Vitamin D Excess:

There are many potential symptoms of vitamin D excess: Nausea, vomiting, constipation, anorexia, abdominal pain, excessive thirst, excessive urination, fatigue, weakness, irritability, difficulty concentrating, depression, psychosis, headaches, bone pain, backache and arrhythmias. Excess can also lead to kidney failure and even death. Some statins  (cholesterol medications) can increase vitamin D levels in your body.

Signs and Symptoms of Vitamin D Deficiency:

There are also many symptoms of vitamin D deficiency: Fatigue, poor overall mental and physical performance, illness/infection, poor wound healing, bone and joint pain and loss and weakening/osteopenia/osteoporosis (long-term deficiency), brittle nails, back pain, myalgia, muscle cramps, tremors, obesity, cognitive problems/difficulty concentrating, insomnia, depression, hair loss, stomach problems, increased cardiovascular disease, erectile dysfunction bariatric surgery, deformities, and cardiomyopathy, among others.

Other Causes of Vitamin D Deficiency:

Besides lack of sun and inability to convert vitamin D (above), there may be conditions that decrease gastrointestinal absorption of vitamin D like Crohn's, celiac, ulcerative colitis, short bowel syndrome and others. Kidney or liver failure, pancreatic insufficiency (chronic), certain cancers, inheritance, malnutrition and various medications (for example steroids - including inhaled steroids; some anti-seizure medications, rifampin for TB, laxatives, bile sequestering agents like Cholestyramine), and obesity can 

Sources of Vitamin D

As mentioned above, one of the most significant contributors to Vitamin D in our bodies is the sun. Our lack of sun or factors that block the sun's rays contribute enormously to low vitamin D levels.

A simple blood test (see below) can determine your need for vitamin D. In the absence of a vitamin D level, according to the Epocrates references the following are recommended daily doses:

• Age 9-70: adequate intake, 600 IU/day to 1000 IU/day (the latter for people with little sun exposure). 

• People over 70-

• Age 71+ years: adequate intake, 800 IU/day

• Doses may be higher in those with malabsorption syndromes, vitamin D deficiency, and other deficiency risks mentioned above. Speak to your healthcare provider

• The maximum safe upper level of intake is 4,000 IU/day unless otherwise directed by your healthcare provider.

Ideally, in the presence of symptoms (above), the recommended level of vitamin D intake should be tailored to the individual. In some circumstances, a high normal blood level may be ideal.

Sources of Vitamin D:

The sun is one of the most beneficial sources of vitamin D. And, it's free. Different sources suggest different daily amounts of sunlight a person should have to maintain optimal vitamin D levels; however, they all recommend between 5 to 30 minutes (average around 15 minutes) of midday sun between 10 am and 3 pm. It really depends on the individual. For example, older people will need more time in the sun; those with obesity also need longer exposure, light-skinned people need less time, darker-skinned people will need more time, and those who live in the north may need more time within this range.

 

Medicinal Forms of Vitamin D

Capsules, topical preparations, tablets, drops, sunlingual, injectable

Note: Your body stores vitamin D, so it is not advised to take vitamin D above the upper limits

unless advised by your healthcare provider/based on lab results.

Recommended Brands

• Doctor's Best® Vegan D3 2,500 IU capsules (Available through this Amazon link)

• Garden of Life Vtamin Code Raw D3 5000 IU capsule (very high dose) (Available through this Amazon link)

• Kirkland Signature [Costco] D3 50 mcg (2000 IU) softgel (available over-the-counter at most Costco stores)

• Nature Made® D3 1,000 IU (25 mcg) softgel (available over-the-counter at many retail pharmacies)

• NOW® High Potency Vitamin D-3 2,000 IU softgel (available through this Fullscript link)

• Vitacost® Vitamin D3 125 mcg (5,000 IU) softgel - very high dose (order through this Amazon link)

• Nordic Naturals® Vitamin D3 Gummies - Great Wild Berry Taste-1000 IU (avilable through this Fullscript link)

• Carlson® Super Daily® D3 2,000 IU - liquid (available through this Fullscript link)

• Pure Encapsulations® Vitamin D3 Liquid 1000 IU (available through the Fullscript link here)

• Source Naturals® Vitamin D-3 - 2000 IU (avilable though the Fullscript link here)

Please Note: We only recommend herbal and supplement brands that meet high standards for safety, quality, and transparency. I research each product before sharing. Some links — like those to Amazon or Fullscript— are affiliate links, meaning I may earn a small commission if you buy through them, at no extra cost to you. It helps support my website, Web Guide to Healthcare. Plus, these links often offer discounts for you, fast shipping, and helpful reviews.

Various foods also provide additional sources of vitamin D:

• Tuna canned in water

• Sardines canned in oil

• Salmon

• Mackerel

• Dairy products like milk or yogurt (Vitamin D fortified)

• Beef or calves' liver

• Egg yolks

• Cheese

• Cod Liver Oil

• Fortified foods (i.e., breads, milk, juices)

• Mushrooms (exposed to UVB light postharvest)

• Oat, almond, soy

Blood Tests for Vitamin D:

Testing can be expensive (average is $50-$75 cash - and labs will likely charge your insurance company even more). Whatever happened to the concept of prevention? Let's catch this problem before it takes a toll. 

If you want to check your vitamin D levels? You have a few options: You can: 

• Ask your healthcare provider to order it

• Make an appointment directly with a lab without a doctor's order - like Quest or Labcorp 

• Order an at-home test from a CLIA-certified lab like our affiliate HealthLabs.com (HSA, FSA, card, no insurance)-they will send a testing kit to send back to them for analysis, typically with a 1-3 day turnaround time. Good if you don't have time to go to the lab.

Q&A

Can I get vitamin D from the light of a tanning bed?

Maybe a little bit, but never as much as the sun because it uses a different UV light. The risks of the tanning bed outnumber the benefits of using one (risks: premature skin aging and an increase in skin cancer, especially melanoma).

If I use suntan lotion, will I still be able to absorb vitamin D?

It may block some of the UV light that increases vitamin D. That is, the benefits of a sunblock to  prevent skin cancer likely outweigh the risks of lower vitamin D levels (if there is any question, supplement).

Can I get vitamin D by sun exposure through a window?

No.

*ConsumerLab is a great third-party testing resource which cites very helpful studies on Vitamin D and many other supplements. It is available on a trial basis - otherwise, through a paid prescription. This is not a paid advertisement - just a recommendation.

Disclaimer: The material above is for informational purposes only. This information is not intended to diagnose or treat a condition. The uses listed above are tentative; some have or are undergoing research trials, but many are not FDA-approved. It is essential that you investigate these supplements further before deciding to use them. Check interactions and contraindications on sites like Drugs.com or WebMD. Do not attempt to treat a serious condition like liver, kidney problems, high blood pressure, heart disease, cancer, diabetes, or thyroid issues without discussing it with a healthcare provider first. If you are pregnant, do not use supplements without discussing it with your healthcare provider.