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Do you supplement with 2,000–5,000 IU of vitamin D each day? Or, do you use your lunch hour every day to lie in the sun? If not, you’re likely low in vitamin D.

You could be raising your risk of developing a plethora of health problems, including diabetes, arthritis, dementia, bone loss, and the flu, just to name a few.

More than half of the world’s population is deficient in vitamin D, and as many as four out of five people in the United States may be below optimal levels.

Fortunately, the most common micronutrient deficiency in the world is easily preventable. High-quality supplements are inexpensive, and if you live in the right latitude, you can get a healthy dose from moderate midday sun exposure.

After reading this article, you’ll understand why vitamin D is one of our Foundational Five, the best supplements for foundational health.

In all my many years of practice of medicine, I’ve never seen one vitamin, even vitamin C, have such a profound effect on human health.

Dr. Soram Khalsa, board-certified internist and medical director of the East-West Medical Research Institute

What Is Vitamin D?

Vitamin D is actually a pro-hormone, not a vitamin. It influences the expression of more than 200 genes and acts as a precursor to hormones such as DHEA and cortisol.

The active form of vitamin D is 25-hydroxy vitamin D, or 25(OH)D.

Through your diet, you consume vitamin D in two forms: ergocalciferol (D2) and cholecalciferol (D3). However, even if you eat fortified foods, the amount you consume through diet is a fraction of what you need each day.

Ergocalciferol comes from plants and is not converted to active vitamin D in the body very well. Cholecalciferol comes from animals and is the best form for increasing 25(OH)D. It’s also the form most researchers use.

Of course, food and supplementation aren’t the only ways to raise vitamin D levels. Since the time of Adam and Eve, sun exposure has been our main supplier.

In ancient Egypt, Greece, Rome, Babylon, and Persia, sunlight (heliotherapy) prevented and treated various medical conditions.

Juzeniene A, et al.

When your skin is exposed to sunlight, UVB rays stimulate the production of vitamin D.

To benefit from the sun’s rays, you need to live close to the equator and expose most of your skin to the midday sun for 20 to 30 minutes. That would give you about 10,000 IU, or 200 times the amount in a glass of fortified milk.

Today, we get more light from our computer screens and cell phones than light from the sun (a topic for another time, but that type of light could cause far more damage than an occasional sunburn). Even when you get out in the sun, you’re probably covered in so much sunblock that you can’t benefit from the UVB rays anyway.

Effects of Low Vitamin D

Spending your days indoors limits vitamin D, but it’s not the only cause of low levels.

Liver and kidney dysfunctions compromise the conversion of cholecalciferol to active vitamin D. Also, certain medications like statins, and plant compounds interfere with absorption of vitamin D.

Cholesterol and vitamin D are absorbed in similar ways. Medications and plant compounds that interfere with cholesterol uptake also interfere with vitamin D absorption.

The Flu

A British doctor named R. Edgar Hope-Simpson was the first to connect low vitamin D and the flu. He observed that in both hemispheres, cases of the flu rise in late fall and early winter, which is the same time period where vitamin D levels drop from their summertime high. His observations were correct.

In one study, supplementing with 2,000 IU of cholecalciferol has been shown to lessen the occurrence of cold and flu symptoms.

In another study, children in Japan took 1,200 IU of cholecalciferol or a placebo from December 2008 through March 2009. At the end of the study, 18.6% of the placebo group and 10.8% of the vitamin D group got the flu. That’s a 42% reduction, using an amount that still isn’t enough to reach optimal vitamin D levels in most people.

Interestingly, the CDC found that a flu shot was only effective in 23% of people who got it based on 2014 data.

Insulin Resistance and Diabetes

Excessive carbohydrate consumption causes insulin resistance and diabetes. However, low vitamin D may make it harder for your body to handle carbs, making it more likely you’ll develop carbohydrate intolerance.

Research shows low vitamin D increases the risk of developing metabolic syndrome by 52%. Raising levels in those with insulin resistance has been shown to reduce symptoms of insulin resistance.

Not surprisingly, obese people tend to have the lowest levels of vitamin D, and since insulin resistance and obesity are often tied together, optimizing vitamin D may help improve body composition. Of course, it won’t do it alone. You still need to follow an effective nutrition and exercise program.

Heart Disease

Vitamin D reduces the buildup of cholesterol in macrophages, white blood cells that attempt to repair damaged heart tissue. Without sufficient D, the macrophages turn into foam cells, laying down fatty deposits and causing atherosclerosis.

Interestingly, some statins have been shown to increase vitamin D levels, which could be one of the ways statins improve patient outcomes in the small percentage of people who seem to benefit from statins. I’m not saying statins are appropriate for everyone, by the way.

Osteoporosis and Bone Fractures

Calcium has been the poster child for bone health for decades. Yet, without sufficient magnesium and vitamins K and D, taking tons of calcium is pointless. In fact, excessive calcium supplementation without magnesium, D, and K could lead to significant health problems.

Vitamin D mediates calcium absorption. And don’t forget, high-protein diets also support better bone health.

Other Effects of Low Vitamin D

The following is part of a growing list of complications connected to low vitamin D.

This is like the Holy Grail of cancer medicine; vitamin D produced a drop in cancer rates greater than that for quitting smoking, or indeed any other countermeasure in existence.

Dennis Mangan, clinical laboratory scientist

Vitamin D is a precursor to adrenal steroid hormones, including DHEA, androstenedione, and cortisol. Though it hasn’t been studied much, it’s likely that insufficient vitamin D could affect the formation of these hormones.

  • Decreased strength
  • Increased body fat
  • Low birth weight of newborn babies
  • Multiple sclerosis
  • Psoriasis
  • Rheumatoid arthritis
  • Schizophrenia
  • Type I diabetes

What Are Optimal Vitamin D Levels?

The table below shows the risk ranges typically referenced by doctors and lab testing companies.

Risk Category ng/mL nmol/l
Deficient <20 <50
Insufficient 20-29  50-72
Adequate >30 >73

Unfortunately, these levels should have been thrown out with tube TVs. The term “adequate” should probably be replaced with “survivable,” and definitely shouldn’t be mistaken for “sufficient.”

The vitamin D council recommends the following ranges based on the most current research.

Risk Category ng/mL nmol/l
Deficient <40 <100
Sufficient 40-80  100-200
High Normal 80-100 200-250
Undesirable 100-150 250-375
Toxic >150 >375

Remember, the average person’s vitamin D level is only 16–25 ng/mL

If your doctor won’t order a vitamin D lab test for you, find another doctor, or just order your vitamin D test yourself (along with the other lab markers you should get tested regularly).

How to Choose a Vitamin D Supplement

As I mentioned above, you’ll find two forms of vitamin D in dietary supplements: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

D2 comes from plants, so vegan supplements contain this form. However, it’s incredibly ineffective.

Supplementing with vitamin D2 to raise your blood vitamin D levels would be like using an eyedropper to get rehydrated after a trek across the desert. Don’t waste your time and money, even if it’s “vegan.”

To become 25-hydroxy vitamin D, D2 must be converted to D3, and the human body does a very poor job at that. Just take D3.

Researchers almost always use cholecalciferol to study vitamin D’s effects on the body. It is most often extracted from sheep’s wool.

Having said that, not all cholecalciferol is the same. Pure vitamin D is incredibly small. It’s so small that raw material suppliers, the companies that make the ingredients for supplement manufacturers, usually dilute it to make it easier to work with.

Most of the time, they dilute cholecalciferol with lactose, BHT, BHA, sodium benzoate, or sorbic acid.

Here’s where it can get misleading. Since the raw material the supplement company orders is cholecalciferol, and the lactose is only included to dilute the nutrient, the lactose does not need to be disclosed on the label of the finished product.

When you buy cheap vitamin D, it’s probably diluted with lactose or one of the other questionable materials mentioned above. If you have lactose intolerance, you could end up scratching your head, wondering why you have constant diarrhea even though you don’t consume milk.

This is one of the benefits of Life Time’s Vitamin D+K. We use cholecalciferol that isn’t diluted with lactose.

To maintain optimal vitamin D levels, the vitamin D council recommends:

  • Children: 1,000 IU per 25 pounds of body weight
  • Adults: 5,000 IU including pregnant and breastfeeding women
  • Upper limit (for us Northerners): 10,000 IU per day

Note: Some people prefer taking cholecalciferol less frequently. Since it is a fat-soluble vitamin, some practitioners suggest that 70,000 IU once a week could be equally effective as 10,000 IU per day. However, more research needs to be done to prove this out. At this point, I would recommend using it daily instead.

Frequently Asked Questions

What are the best sources of vitamin D?

The best sources of vitamin D are exposure to sunlight (without sunblock) and dietary supplements. Food sources, even when they’re fortified, contain very little vitamin D.

How much vitamin D should you get?

Your dietary need for vitamin D varies based on your sun exposure and skin type. However, most people need much more than the 400 IU–800 IU commonly found in foods. The Vitamin D Council suggests about 5,000 IU per day for most people.

Are vitamin D supplements vegan?

Most vitamin D comes from the skin of fish, or from sheep’s wool, so it is animal-sourced. However, it’s possible to get vitamin D from plants called lichens, so more companies will likely offer this type of vitamin D to satisfy the needs of the vegan market.

Your Vitamin D Summary

If you scrolled right to the bottom of this article looking for the summary, here are the key points you need to know:

  • You are very likely low in vitamin D, and it can compromise your health in a myriad of ways, from body composition to cardiovascular health and cancer, and in fighting off the flu to reducing fracture risk.
  • Your doctor should be more than willing to test your vitamin D levels, and if he or she won’t, find a different doctor or order your own lab testing.
  • If you were hoping to find a good food source of cholecalciferol, there isn’t one.
  • To optimize your vitamin D, move near the equator and lie out in the sun for a half hour each day in your loincloth, or for better results, bare naked. Or, start supplementing with a high-quality vitamin D supplement.

If you missed it at the top, vitamin D is one of our Foundational Five. Check out the other four in our article on the Foundational Five, the best supplements for foundational health.

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