Vitamins: All You Need to Know

By Phoebe Chi, MD, MPH

Multivitamins. Have you ever wondered if taking one makes a difference? Whether you even need one? And if you take several supplements, how much should you take of each…and when? In this post I will answer these important questions as well as provide you some tips on finding the perfect supplement for your needs.


– Step 1 –
Determine Your Need

One of the first things to consider when deciding whether or not you need a daily multivitamin is your diet. If you are pretty healthy and already eat a diet that includes plenty of fruits, vegetables, whole grains, protein, and healthy fats, chances are you likely already receive the nutrients that you need from your foods. In this case, studies show that a multivitamin may, in actuality, add little or no benefit to your health. Ask yourself: how does your diet compare to the diagram below?


Of course, even if you do follow a well-balanced diet, sometimes your body—for various reasons—simply needs more than what your meals can provide. While the evidence is somewhat conflicting—some studies show slight benefits while others don’t—I still believe that for most people, the potential health benefits of taking a daily multivitamin outweigh the potential risks. For this reason, some physicians like to think of a daily multivitamin in terms of it being a ‘micronutrient insurance.’ Nevertheless, this next section will help you determine if taking a multivitamin, and what kind, is best for you…

Do You Fall into These Groups?

Consider taking a multivitamin if you are:

  • Over 50 years of age
  • A woman of child-bearing age who might get pregnant
  • A woman who experiences heavy bleeding during menstrual periods
  • Pregnant or breastfeeding
  • On a low-calorie diet (less than 1,600 calories/day) or have a poor appetite
  • Vegan or strict vegetarian
  • Someone who uses alcohol or tobacco heavily
  • Someone who experiences chronic diarrhea or has a disease of the liver, gallbladder, intestines or pancreas
  • Someone who has had gastric bypass surgery

BUT, talk to your doctor first if you are:

  • Taking blood thinners: If you take warfarin (Coumadin), any supplement/food with vitamin K can lower the medication’s effectiveness. Therefore, always discuss with your doctor before starting one, as your dose may need to be adjusted or your level closely monitored.

Be CAUTIOUS if you are:

  • A smoker: Avoid multivitamins providing large amounts of vitamin A in the form of beta-carotene because a few studies have linked these nutrients to an increased risk of lung cancer.
  • Already taking other supplements: If you consume fortified foods and drinks (those with added vitamins and minerals) or take other dietary supplements, make sure that the multivitamin doesn’t cause your intake (especially vitamin A and iron) to go above the UL value (see below).

How Much is Too Much?

The Tolerable Upper Intake Level (UL) is the maximum amount of daily vitamins and minerals that you can safely take without risk of an overdose or serious side effects. This is a useful measure to refer to if you are taking multiple supplements and want to know if you are getting too much of something. The available UL for common nutrients are provided below for your reference.

Be aware that some vitamins and minerals are riskier than others. Vitamin A, D, and E are a few that you should be more cautious about. Since they are considered fat-soluble, extra amounts accumulate in your tissues rather than excreted, potentially leading to toxic levels and negative health effects. This is why it is easier to overdose on vitamin D than, say, vitamin C (which is water-soluble and gets flushed out). Therefore, be careful to never take more than the recommended UL unless instructed by a physician (eg. for correcting a deficiency). Other riskier supplements to keep in mind include iron and selenium.


– Step 2 –
Choose Your Multivitamin

Check the Contents

When choosing a multivitamin, try to find one tailored to your age, gender, and other characteristics (e.g., pregnancy). This is because there are important differences. For example, multivitamins for men often contain little or no iron, whereas those for seniors provide more calcium, vitamins D, and B12 than those for younger adults, and prenatal supplements generally have no vitamin A in the form of retinol.

On the label of every supplement, you will find the Percent Daily Value (%DV) This will serve as one of your main guides in selecting a multivitamin:

◊ What to look for on the label:

  • 100% of the DV for these vitamins: Vitamin D, B1 (thiamin), B2 (riboflavin), B3 (niacin), B12, and folic acid.
  • Up to 100% of the DV for these minerals: Copper, zinc, iodine, selenium, and chromium.
  • At least 100mg of magnesium.
  • Lower levels of vitamin A: Try to find one with no more than 3,000 IU. Some studies have shown that getting more than 6,000 IU of vitamin A (food + supplements) may increase your risk of fractures. Beta carotene is safe for your bones, although high doses may increase the risk of lung cancer in smokers.
  • For premenopausal women: Look for a product that provides 100% of the DV of iron.
  • For men and postmenopausal women: Choose a multivitamin without iron.
  • Don’t scrutinize the calcium: The amount in multivitamins is usually low, because calcium is simply too bulky for one pill. Therefore, depending on your diet and risk factors, you may benefit from a separate calcium supplement.

Below is a sample label. Would this supplement be right for you?


Check for Quality

In shopping for a multivitamin, more expensive (including ‘designer’ supplements) doesn’t necessarily mean more benefits, and standard store-brand supplements are usually just as good.

◊ Tips for ensuring a quality product:

  • Look for “USP Verified”on the label: The initials “USP” ensure that the supplement meets the standards for strength, quality, and purity established by the testing organization U.S. Pharmacopeia.
  • Avoid megadoses: High-dose supplements increase your risk of building up toxic levels of nutrients in your body.
  • Beware of extras: Don’t give in to the temptation of added herbs, enzymes, amino acids, or unusual ‘special’ ingredients. These additions usually add nothing but cost. In some instances, they may adversely interfere with medications or medical conditions. For similar reasons, ignore products that carry these terms: “high-potency,” “stress formula,” “starch-free,” “natural,” or “slow-release.”
  • Check the expiration date: Supplements can lose potency over time, especially in hot and humid climates. If a supplement doesn’t have a date, don’t buy it.

As with all supplements, check with your doctor first before starting a multivitamin, especially if you have health problems or are taking any medications (eg. blood thinners). At your next checkup, take all of your supplements along so that your doctor can review and discuss whether you’re taking the right types and amounts.

– Step 3 –
Make Your Daily Regimen

If your only supplement is the multivitamin, you can take it with any meal that’s convenient. However, if you are currently taking other supplements such as fish oil, calcium, magnesium, iron, zinc, or probiotics, refer to the diagram below to determine the best time to take yours (note: vitamin D can be taken with your multivitamin during a meal):


And with that, you’re all set. Here’s to healthy living!

32 thoughts on “Vitamins: All You Need to Know

Add yours

  1. What about herbal supplements. Since there really isn’t regulation on them, we could be taking something that isn’t even in the product. I used ti take a lot of them, but it gets to be expensive Right now I am only taking flaxseed oil, elderberry and oil of oregano.
    I just checked my multi vitamin, thanks for reminder, and it expired in 2015, so that will be tossed..
    I am also taking B-12 5,000 mcg, acidophilus,and two different ones that are supposed to contain vegetables and another one with fruit. Half the time I forget to take them at all.
    That is why the multi vitamin was expired. For a long time, I thought the fountain of youth and perfect health were in exotic herbal supplements. I spent a fortune on them.

    Liked by 1 person

    1. For herbal supplements, I usually don’t feel comfortable recommending them straight out–simply because, like you pointed out, the quality and potency of them can be so unpredictable. On top of that, those supplements can often interact with each other and with medications. But if what you are on works for you, that’s great! But I do understand how it can get expensive…

      Liked by 1 person

      1. There’s so much information that regularly comes out abut the latest super supplements like turmeric is the rage right now. I would think that if they were plant based they would have some benefits. I mean, aren’t many medicines plant based? I’m sure if you were to use the real plant it would have more benefits, but then as you say it could interact with something else you are taking.
        Have you ever heard of Ray Kurzweil? He’s a futurist and inventor among other things. At one time he was on a regime of over 250 supplements, supposedly he is down to 150. He has some strange ideas, but he has a lot of followers.

        Liked by 1 person

        1. Wow…250 is quite a lot! 😲

          Yes, herbal supplements can definitely be effective and powerful treatments for things. I think some docs are just hesitant to directly recommend them because the science behind them (the quality of research) is unfortunately lacking, so it’s hard to fully inform someone of their benefits and risks. But my attitude is…if it personally works for you, I think it’s great!

          Take care!


  2. Very informative kind of article, thank you.

    “You, my carrot, Brutus?” I really did not know that higher doses of beta-carotene and lung cancer have some interdependence of the negative sort…


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