Vitamin D: Answers to Common Questions

PJ Hamel Health Guide
  • What’s the difference between vitamin D and vitamin D3? What’s a d-25 hydroxy level? Are there side effects to taking vitamin D supplements? Quick answers to your questions about vitamin D, a critical element in good bone health.

    Q. Why the big fuss about vitamin D? How does it help me?


    A. Vitamin D has been the subject of lots of media attention in recent years, being touted as everything from cancer preventive to diabetes cure. Most of these claims, often based on preliminary studies or anecdotal evidence, have yet to be proven.

    But vitamin D’s role in keeping bones strong is well documented. Calcium is the chief element we need to keep bones healthy; and without vitamin D, calcium can’t do its job. Vitamin D both increases the absorption of calcium in your digestive system; and helps maintain the amount of calcium and phosphate in your blood necessary for bone growth.

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    Q. What’s my goal for daily vitamin D consumption?

    A. The government’s Food and Nutrition Board (FNB) has set the current Recommended Dietary Allowance (RDA) average daily intake for most adults to 600 IU (800 IU for those over 70 years old). This assumes a minimal amount of sun exposure (see below).

    Q. How do I know if I have enough vitamin D in my system?

    A. Via a blood test. The results will show your level of 25-hydroxy vitamin D (“25-hydroxy” simply being the scientific name for the type of vitamin D measured).

    Beware, though, that insurance may not cover the test; Medicare has been considering limiting testing to individuals with certain health conditions. So check with your doctor about the cost of the test, and determine from your insurance carrier whether it’s covered.

    Q. What’s the best way to get vitamin D – via a daily supplement?

    A. Since vitamin D isn’t found naturally in a wide range of foods, the most reliable way to meet your daily needs is probably via supplement.

    However, the easiest way is simply by exposing your skin to sunlight. There are no hard and fast rules for a minimum amount of sun exposure necessary for your body to produce adequate levels of vitamin D; there are simply too many variables among skin color, where you live, weather, etc. In addition, prolonged exposure to sunlight’s UV rays has been shown to cause skin cancer.

    But the National Institutes of Health, via its Office of Dietary Supplements, states that as little as 10 to 15 minutes of sun exposure twice a week, between mid-morning and mid-afternoon, may be enough. This is outdoor sun (not through a window); and without sunscreen. 

    If you’re looking to supplement vitamin D via your diet, regular servings of fatty fish (tuna, mackerel, sardines, salmon); eggs yolks (whole eggs, not egg substitutes); beef liver, cheese, and vitamin D-fortified milk are the best sources. Look for D-fortified cereal, margarine, and orange juice, as well.

    Q. Is “25 hydroxy” vitamin D, or D2, or D3, or… What type of vitamin D should I be looking for?

    Vitamin D is available in two main forms: vitamin D2 (ergocalciferol), which comes from plant sources; and vitamin D3 (cholecalciferol), which comes from other foods, like fish; and from exposure to sunlight.

  • Researchers are in mild disagreement about differences in effectiveness between vitamin D2 and D3; some studies have shown that D3, the type naturally synthesized by humans, works better and has a more lasting effect than D2. But other studies have shown no difference between them.

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    Vitamin D3 is the type included in most supplements and fortified foods.

    Q. Is it possible to get too much vitamin D? Do I need to worry about an overdose?

    A. If your vitamin D level needs to be raised, consider increasing your intake of supplements – but don’t go above 4,000 IU daily, between diet and supplements. According to the FNB, “megadosing” with vitamin D is ineffective – and may actually be harmful.

Published On: September 22, 2011