Vitamin D: Does Megadosing Help?

PJ Hamel Health Guide
  • Vitamin D has been touted of late as helping prevent everything from osteoporosis (it does), to cancer (it might), to cardiovascular disease (the jury’s out). With its newfound fame, vitamin D has engendered a group of followers claiming “more is better” – why limit yourself to the recommended 600 IU daily, when 10,000 IU or more could provide even greater protection against disease? We look at the risks of so-called “megadosing,” and examine levels suggested by the government’s Food and Nutrition Board.

    Do you take a vitamin D supplement?

    If not, you probably should consider it. Vitamin D works hand in hand with calcium to help preserve bone health. Neither can do the job alone; but together, vitamin D and calcium are our best safeguards against osteoporosis.

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    What’s the “ideal” level of vitamin D you should have in your body? And how do you reach and maintain that level?

    The amount of vitamin D in your system is measured with a simple blood test: the hydroxy-25 vitamin D test. Here are the current recommended levels* set by the Institute of Medicine, a division of the National Academies:

    •Less than 30 nmol/L – associated with vitamin D deficiency, leading to rickets in infants and children and osteomalacia in adults;
    •30-50 – generally considered inadequate for bone and overall health in healthy individuals;
    •greater than 50 – generally considered adequate for bone and overall health in healthy individuals;
    •greater than 125 – emerging evidence links potential adverse effects to such high levels, particularly greater than 150.

    *Taken from the Office of Dietary Supplements/National Institutes of Health Web site.

    So you’ve had your vitamin D blood test, and it shows you’re at 40 nmol/L – which puts you below the “generally considered adequate” threshold. What do you do?

    You work at getting more vitamin D into your system. But how much do you need to raise your level – and should it be in the form of food, supplements, sunlight… or all three?

    These are questions that have had nutritionists and researchers at odds for several years now. The Institute of Medicine is mother organization to the Food and Nutrition Board (FNB) – which sets Dietary Reference Intakes (DRI) that are then translated to the “% Daily Value” (%DV – the amount you should take daily) you see on the side of your bottle of multivitamins.

    The FNB is the official governmental arbiter of how much vitamin D – and calcium, and vitamin C, and every other vitamin and mineral – we should take to ensure we have a healthy supply in our bodies. The FNB updated the DRI/%DV for vitamin D in 2010 – amid much speculation concerning just how much that number would increase, given the growing number of health claims being made on vitamin D’s behalf.

    And the answer is – not much. The FNB decided to play it safe, upping the Recommended Dietary Allowance (RDA) average daily intake for most adults to 600 IU (800 IU for those over 70 years old) – a 50% increase over the previous 400 IU, but well below the 1,000 IU many nutritionists and doctors had hoped for. 

  • So, 600 to 800 IU vitamin D is what you should shoot for daily. This amount should be sufficient to maintain bone health in normal, healthy people, and takes into consideration minimal exposure to sunlight – which is what most of us get, between lack of outdoor activities and use of sunscreen.

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    Considering the difficulty of eating enough vitamin D-rich foods, supplements are the most reliable, “trackable” way to ensure vitamin D consumption. So let’s look at supplements.

    Vitamin D is always present in a multivitamin – you’ll find it listed as vitamin D3, or vitamin D (cholecalciferol), which are the same thing; or vitamin D (ergocalciferol), which is vitamin D2. According to the Office of Dietary Supplements, either is acceptable.

    The amount of Vitamin D in most supplements ranges from 600 IU to 1,000 IU. So a multivitamin should cover your recommended daily needs – even without exposure to sunlight, or taking into account vitamin D in the foods you eat.

    But let’s get back to your blood test; you’re below the acceptable vitamin D level. Should you go beyond that simple multivitamin, and start ingesting more vitamin D to bring your level up?

    Well, the definition of “more” can be complicated. If you’re taking vitamin D2, for example, it’s less potent in higher doses than vitamin D3. And studies show that the higher the dose, the less overall effect it has on your vitamin D level.

    Furthermore, more isn’t always better. Remember those recommended levels of vitamin D set by the FNB? Although levels greater than 50 and less than 125 are considered optimum, studies show that levels as low as 75 can result in an increased risk of cancer; heart problems; and falls and fractures in the elderly.

    So, let’s get back to your vitamin D blood test, showing you with a level of 40. Some doctors recommend up to 50,000 IU weekly, for patients trying to increase vitamin D levels. Is this “megadosing” safe?

    Not according to the FNB. The Tolerable Upper Intake Level (e.g., the maximum amount you should take daily) is 4,000 IU for vitamin D – far above the 800 IU recommended, but also well below the weekly 50,000 IU prescribed by some health professionals.

    Bottom line: If you’re a healthy person trying to maintain a normal, healthy amount of vitamin D in your system, a daily supplement giving you 600-800 IU vitamin D is fine.

    If your vitamin D level needs to be raised, consider more potent supplementation – 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.

    When it comes to vitamin D supplementation, the official governmental stance is “better safe than sorry.” 

Published On: August 23, 2011