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Vitamin D deficiency & toxicity: Where to draw the line?

Just because a little of something is good, is more of it even better? What should we do with the new research showing that vitamin D3 supplements are twice as effective as vitamin D2? Should we all take “more?” How much is enough? When does too much become dangerous?

First, what exactly are vitamins and minerals, and why are they important? From PrecisionNutrition we learn that vitamins:

  • Are organic compounds that are essential in micro amounts for supporting normal physiologic function.
  • Are natural components of foods; usually present in very small amounts.
  • Are essential for normal physiologic function (e.g., growth, reproduction, etc.).
  • When absent from the diet, they will cause a specific deficiency.
  • Are generally categorized as either fat-soluble or water-soluble depending on whether they dissolve best in either lipids or water.
  • Serve a variety of roles in the body – one of the most important being their roles as cofactors for enzymes – called coenzymes.

There are 13 vitamins—vitamins C, A, D, E, K, and the B vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, B6, B12, and folate).

Besides food, humans obtain vitamins as:

  • Microorganisms in the intestine — commonly known as gut flora—produce vitamin K and biotin.
  • Vitamin D3 is synthesized in the skin with the help of natural ultraviolet (UVB) sunlight.
  • Some vitamins can also be obtained from dietary precursors. Examples include vitamin A, which can be produced from beta-carotene. Niacin is produced from the amino acid tryptophan.

[As for minerals, most are considered essential, meaning we need them in our diet.  Minerals are divided, reflecting how much the human body requires — major minerals (macrominerals) and trace minerals (microminerals). For example, iodine, zinc and chromium are necessary in micro-amounts; we require much larger amounts of calcium, sodium, potassium, and magnesium.]

Until the 1900s, vitamins could only be obtained by eating food. However, they are now commercially available as supplements.

Vitamin D: The Sunshine Vitamin

The major role of vitamin D is to maintain normal blood levels of calcium and phosphorus and keep them in balance to support and maintain healthy bones.

Vitamin D3 (cholecalciferol) is found in animal-sourced foods, such as cod liver oil, fish, egg yolks, and whole milk dairy, and synthesized in the skin of humans and animals. Before the 20th century, it was estimated that humans obtained 95% of vitamin D3 through sun/skin synthesis. Since the middle-late part of the 20th century, research demonstrates that it could be as low as 15-25%.

Vitamin D2 (ergocalciferol), is synthesized by plants, such as mushrooms, and is the form most often used to fortify foods such as milk.

In the body, the initial form of vitamin D (7-dehydrocholesterol) travels to the liver and converted into another slightly more active form of vitamin D called 25-hydroxyvitamin D. This is the form of the vitamin that doctors are testing for when assessing deficiency.

From the liver, it travels to the kidneys where it is converted into the highly metabolically active form of vitamin D called calcitriol, or 1,25 dihydroxyvitamin D.

At this point, it is no longer considered a vitamin but rather, a steroid hormone, similar to other steroid hormones such as estrogen, testosterone, and cortisol.

Article continues below graphic.

Global Deficiency of Vitamin D? Why?

Health experts report that vitamin D deficiency is a “global health problem” and as reported in the International Journal of Health Sciences, “Over a billion people worldwide are vitamin D deficient or insufficient.”  A review paper published in 2011 indicated that despite the abundance of sunshine, vitamin D insufficiency may be a public health problem in Latin America and the Caribbean, “but the exact magnitude is currently unknown.”

An extreme and prolonged deficiency of vitamin D causes rickets, resulting in soft bones and bowed legs in children. In adults, prolonged deficiency can lead to osteomalacia.

Low levels of vitamin D are associated with increased loss of muscle strength and mass as we age, increased risk for cancers, lower immunity, high blood pressure, development of neurological disorders, and development of diabetes.

You’re more at risk for deficiency if you suffer from medical conditions including Crohn’s disease, cystic fibrosis, and celiac disease: they can affect the intestine’s ability to absorb vitamin D from foods.

Because of the awareness of potential dangers of skin cancer, people are using more UVB-blocking sunscreen, blocking the skin’s ability to manufacture D3.

Obese and overweight people may have a more difficult time maintaining optimal limits of D; since vitamin D is a fat-soluble vitamin, subcutaneous fat may sequester the vitamin (read more here.)

Vegans may be at increased risk since they avoid the most bioavailable dietary sources of vitamin D3, including fish and fish oils, egg yolks, fortified milk, and liver.

Some medications can decrease activity of vitamin D in the body including anticonvulsants, bile acid sequestrants, GERD medications, corticosteroids and heparin.

Seniors may be at high risk for deficiency, due both to the decrease in time in the sun/sun exposure, but also because a person over 70 produces about 30% less vitamin D than a younger person with the same sun exposure. As people age they’re less able to convert vitamin D to its active form.

How to tell if you have enough D? How Much Do We Need?

Vitamin D lab tests generally assess the total volume of 25-Hydroxyvitamin D (25OHD), which is the form of vitamin D circulating in blood. They may also provide information on the levels of vitamin D2 and D3, which comprise total vitamin D levels.

A total serum level of 250HD of at least 20 ng/mL (nanogram per milliliter) is considered “sufficient” by the Institute of Medicine, although scientists do not agree on the optimal reference range. And this number will vary depending on age and health conditions.

A concentration of less than 20 ng/mL is generally considered inadequate, requiring supplemental treatment.

For Optimal Health

Although it’s ideal to obtain all the necessary vitamins and minerals essential for growth and health through diet, it’s not always possible.

According to, “Guidelines from the Institute of Medicine increased the recommended dietary allowance (RDA) of vitamin D to 600 international units (IU) for everyone ages 1-70, and raised it to 800 IU for adults older than age 70 to optimize bone health.”

The safe upper limit was also raised to 4,000 IU.

Doctors may prescribe more than 4,000 IU to correct a vitamin D deficiency.

How Much Is Too Much?

One potential risk of excessively high dose vitamin D is toxicity leading to high levels of calcium in the blood. has published a thorough and well-referenced paper about the delicate balancing act that describes how vitamin D, calcium, magnesium and vitamin A work synergistically. Read the entire paper here.

Vitamin K2 allows the body to use calcium to perform its clotting function. Without sufficient K2, calcium levels can build up increasing risk for vascular deposits and kidney stones.

Magnesium helps modulate the sensitivity of tissues to vitamin D and maintain calcium balance.

Vitamin A is linked to prevention of vitamin D toxicity: if you’re deficient in vitamin A, excess vitamin D can be problematic.

Can supplementation with vitamin D hold some risks?  Yes, it can.

Studies show that people with the highest levels of vitamin D have more bone fractures, fall more frequently, get less sleep, and have a higher mortality rate compared to those with lower, but sufficient, levels. Signs of vitamin D toxicity include chronic constipation, nausea, confusion, kidney stones, and abnormal heart rhythm.

There’s a very important message here. If a little is good, more is not necessarily better. And self-medicating with potentially toxic doses of any vitamin or mineral can have potentially dangerous results. Don’t do it.

How To Increase Your Vitamin D3 Naturally

It resembles sterols in structure and functions like a hormone. During cholesterol synthesis 7-dehydro cholesterol is formed as an intermediate. On exposure to sunlight, it is converted to cholecalciferol (vit D3) in the skin.

The recommendation for natural sun exposure is 15-30 minutes of mid-day sun daily (15 minutes for lighter-skin; 30 for darker skin.) Black people absorb more UVB in the melanin of their skin than do white people and, therefore, require more sun exposure to produce the same amount of vitamin D. Living here in Ecuador near the equator and especially since we live at high altitude means the mid-day sun is stronger: you never want your skin to burn so ten cuidado.

My Cuenca dermatologist encourages no sun skin exposure without UV protection — especially at our Andean altitude.  And of course, the American Cancer Society advises to steer clear from any type of tanning bed.

But in your vigilance in protecting yourself from the harmful effects of UV rays, you’re also at risk for vitamin D deficiency.  What to do?

Consider supplementation

Consider getting tested to see if your vitamin D level is within normal limits. Speak to your doctor about taking a vitamin D supplement, particularly if you have risk factors for vitamin D deficiency, like age, medications, poor diet, and/or any of the diseases that prevent you from absorbing vitamin D.

And lose excess fat stores, so that the vitamin D you do eat is more easily absorbed and metabolized. Getting to a healthy weight can also reduce your risk for type 2 diabetes, heart disease, arthritis, some cancers, and more.

The recommendation consensus for supplemental vitamin D ranges from 600-800 IUs to 2,000 IUs daily, higher amounts for people who are receiving little sun exposure: other factors to consider include age, race, latitude, season, sun exposure, diet, your weight (obese or overweight need more), and more.

The majority of studies that compare the effects of vitamin D2 and D3 confirm that vitamin D3 is better absorbed and utilized, and has recently been shown to be twice as effective in raising vitamin D levels in the body.

Since vitamin D is a fat-soluble vitamin, it’s recommended to take your D3 with your largest meal of the day.

Foods to increase your vitamin D

Animal foods naturally high in vitamin D3 include cod liver oil, and in smaller amounts fatty fish including herring, mackerel, sardines, salmon and tuna, eggs, and whole milk. Fortified foods and dairy and mushrooms are good sources of vitamin D2.

Aim For Synergy: Magnesium, vitamin A and vitamin K all work in concert with vitamin D in the delicate balancing act that supports good health.  Best foods include:

Vitamin K and magnesium: Leafy greens and fermented foods: asparagus, Brussels sprouts, kale, spinach, and Swiss chard are rich in vitamin K1 and also magnesium.

Fermented foods including sauerkraut and soft cheese are rich in K2. Berries, guava, whole grains and brown rice, legumes and lentils, nuts and pumpkin seeds, avocados, bananas, spices including coriander basil, and dill, and dark chocolate are good sources of magnesium. (Check out for nutrient values of different foods.)

Vitamin A: Colorful fruits and vegetables like cooked carrots and sweet potatoes and dried apricots are rich in beta-carotene, the precursor to vitamin A. Egg yolks, liver from any animal, cod liver oil, and egg yolks and dairy from grass fed animals are rich in retinol, the active form of vitamin A.

Vitamin D3 supplements are generally manufactured from lanolin in sheep’s wool or from fish oil and are shown to be more effective at raising blood levels, however, vitamin D2, sourced from plants, can certainly help.

According to, “The difference is that vitamin D3 from animals produces more sustained blood levels of the vitamin.  In contrast, blood levels begin to drop fairly rapidly after just a few days when vitamin D2 is the source of the vitamin.

This matters only if you’re taking very high doses of vitamin D less frequently — like a big dose every week or every month. This is the approach that is sometimes used to correct vitamin D deficiency.

But for vegans who are taking vitamin D2 pills on a daily basis — in amounts close to the RDA of 600 IUs — this plant-derived form of the vitamin is just as good for preventing deficiency and protecting vitamin D status.”

If you’d like to learn much more about vitamin and mineral supplements, and recommendations for brands (available in North America) I suggest subscribing to, the “Leading provider of independent test results and information to help consumers and healthcare professionals identify the best quality health and nutrition products.”  Learn more here.

Sources Product Review: Vitamin D supplements review (including Calcium, Vitamin K, Magnesium.)

Food & Nutrition Bulletin. Less than adequate vitamin D status and intake in Latin America and the Caribbean: a problem of unknown magnitude.

National Institute on Aging: Vitamins & Minerals. Vitamin D guidelines may be changed following new study.  Dermatology Nursing. Vitamin D: A Rapid Review. All About Vitamins & Minerals. Vitamin D supplements: Are yours helping or hurting you? How much vitamin D comes from food, and how much vitamin D comes from sunlight? Vitamin D Deficiency.

13 thoughts on “Vitamin D deficiency & toxicity: Where to draw the line?

  1. In my opinion, this is the finest article you have published in CHL. You are a treasure. I have some observations I will send you privately.

  2. Vitamin D levels are very important. The biggest problem is that if your 25 hydroxy Vit D level is in the low range of normal like 30 you are considered normal. Whereas the optimal value of vit D should be closer to 70-80. It is important that your levels be checked after you are on a steady dose as well as your calcium levels. Persons with low vitamin D are also more prone to developing cancers!!

    Cudos on your well written article!!

  3. I am now reading about Vitamin “G”. I try to keep up with the value of proper nutrition, vitamins and supplements to keep our bodies as well as possible as we age, gracefully hopefully. Just wondering if you know anything about the hype with the “G” vitamin. Thanks for the great info..

    1. Vitamin “G” is Riboflavin, or vitamin B2. Read more on And here’s the history: The naming of vitamins began with Funk’s isolated concentrate. The molecule present here was called vitamin B, since it cured Beri beri disease. Following this, vitamins were name alphabetically: vitamin A was discovered in 1913-1914, and then in chronological order, vitamin C, vitamin D which could cure rickets disease, and vitamin E which was important to fertility. The later discovery of a vitamin required for blood clotting led to the naming of vitamin K where the K denotes koagulation.

      One particular group of vitamins was found to have similar properties and functions, in that they are all coenzymes (aids to enzymes). These are the B group vitamins, which are all water-soluble. Initially, they were given numbers, but as their chemical structures were determined, they were given names which are now increasingly used. A list of the main B vitamins is given below:
      B3Nicotinamide (also Vitamin P or Vitamin PP or Niacin)
      B5Pantothenic acid
      B7Biotin (also Vit H)
      B9Folic acid (also Vitamin M and Vitamin B-c)

      There are also a number of associated chemicals which resemble B vitamins and may or may not have vitamin status. These include choline, inositol and para-aminobenzoic acid, as well as vitamin B15 (pangamic acid) and vitamin B17 (amygdalin)

      1. I also take choline to help with removing sugar from the liver. At least that is what I’ve been told. Even though I’m not over weight by much, and have always maintained fairly healthy eating habits; in the last few years I have had many problems with my joints. I have had several surgeries in the last two years with a partial knee replacement being scheduled as I write this. I have always been very active and have been told that it is probably just hereditary with my joints. I am a firm believer in natural and western medical ways to help keep the body functioning as best as possible. I very much believe that our diets in the US and many other countries with the huge population including children with obesity issues is a large contributor to our health problems. If big PHARM stays out of the way, hopefully the increase in getting the information out to people will help all of us remain as healthy as possible. Gracious.

  4. Vitamin D and its effect on the ejection fraction of the heart.

    A medically and statically accurate study by a UK medical school and published in the Lancet and the NYT found that the “ejection fraction” — the amount of blood pumped from the heart increases when one takes 5000 IU of vitamin D. Ta-Dah!, So all of the benefits SBM details plus ones heart works better.

  5. A friend of mine wrote to me to say that most labs will take your sample, but most will send it out to what we call a “Reference Lab.” He said the best thing to do is ask your favorite lab how they handle the testing. He suggested that one such location (for $25) is:

    Cordero Loyola Marcelo Hernando
    Descripción: Laboratorio de Endocrinología Hormolab
    Agustín Cueva 1-23 Av 12 de Abril


    1. Another wrote to say that she went to the lab on the ground floor of Mt. Sinai Hospital/Tower 1, and requested the test herself (no doctor prescription necessary). She said she paid $40.

  6. You have stated a very medically conservative view of vitamin D3 here. If the appropriate level is just 600 IU per day and exposure for 30 minutes in minimal clothing makes 15,000 IU by noon sun, just imagine how ancient humans must have been falling over with vitamin D poisoning after a couple of sunny days! Anything over two minutes in full sun would qualify as an overdose with these guide lines..

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