For many years, I’ve strongly recommended ConsumerLab.com for evidence-based and trustworthy advice about purchasing or ingesting herbs, vitamins, or supplements. This week I’m running some samples of their wares and encourage you to subscribe to this great site if you take or are considering any natural medicines. Oh, by the way, I have no financial connection to ConsumerLab at all.
This is the “Executive Summary” of ConsumerLab’sRisks of Too Many Vitamins & Supplements.
It IS possible to take too many vitamins and supplements — or too much of a particular vitamin or supplement — leading to adverse effects as well as interactions with other supplements and drugs. In fact, in 2020, there were over 50,000 reports to U.S. Poison Centers of toxicity caused by vitamin supplements including multivitamins, vitamin A, vitamin D, and niacin (AAPCC Annual Report 2020).
The following supplements are among the most common causes of acute toxicity, i.e., from ingesting an extremely high dose in a short period of time:
Although these effects may vary depending on the vitamin ingested, according to some experts, symptoms common to all forms of hypervitaminosis include:
You can check ConsumerLab’s RDA Table to see the Tolerable Upper Intake Levels (ULs) for vitamins and minerals, above which the risk of adverse effects increases. (The table also includes the daily requirements for these nutrients). Be sure to include all of your sources for a particular vitamin (including fortified foods) when calculating your daily intake, especially if you are taking multiple supplements. For example, if you take a multivitamin that provides the recommended daily intake of vitamin A, be aware that by taking cod liver oil or other supplements that contain a high dose of vitamin A, you may be getting too much.
Keep in mind that, over the years, ConsumerLab tests have revealed many vitamin supplements to contain much more (or less) of a vitamin than the amount listed on the labels, which could increase the risk of toxicity. Our tests of multivitamins in 2020, for instance, found that two gummy vitamins contained more than 200% of their listed amounts of folic acid, putting the amount of folic acid from one of these gummies very close to the UL — and consumers taking these gummies could potentially exceed the UL for folic acid if consuming folic acid from other sources, such as a fortified breakfast cereal. The only way to know for sure that a supplement contains the amounts of vitamins listed on the label is if it has been tested by an independent third party like ConsumerLab.
Also, be aware that supplements other than vitamins can pose a risk of overdose. Over the last ten years or so, for example, reports to poison control centers in the U.S. due to ingestion of melatonin increased by 530% among infants, children, and young adults.
The following supplements are among the most common causes of chronic toxicity, i.e., from taking much higher doses than needed over a longer period of time.
Supplements containing herbal or plant-based ingredients such as ashwagandha, cocoa, echinacea, green tea, turmeric, and curcumin, and many others, as well as those containing substantial amounts of minerals, have the potential to be contaminated with toxic heavy metals such as lead, cadmium, and arsenic — which is why ConsumerLab tests these products for heavy metal contamination in its product reviews.0
Some contaminants are specific to particular supplements. In 2022, for example, ConsumerLab tests revealed that 30% of the red yeast rice supplements it selected for testing were contaminated with citrinin, a potential kidney toxin.
Unless the supplements you take have been tested by an independent third party like ConsumerLab, there is no way to know for sure if they contain toxic heavy metals or other contaminants — and taking multiple supplements that have not undergone testing, particularly those containing herbal or mineral ingredients, could potentially increase your exposure.
The more vitamins and supplements you take, the more opportunity there is for interactions with other supplements as well as with medications you may be taking.
For example, taking calcium or magnesium at the same time as iron or zinc may reduce the absorption of iron and zinc. High doses of calcium and other minerals may reduce the absorption of carotenoids, such as beta-carotene, lycopene, and astaxanthin (see our article about which vitamins and minerals should be taken together or separately for more details).
Certain herbal supplements, such as St. John’s wort, can interact with many common medications, including blood pressure lowering medications such as lisinopril (Zestril, Prinivil), and SSRI antidepressants such as citalopram (Celexa), fluoxetine (Prozac), and sertraline (Zoloft). St. John’s wort can also interact with blood-thinning medications such as warfarin (Coumadin), the acid-blocking medication omeprazole (Prilosec), and the antiviral treatment for COVID-19, Paxlovid.
Supplements such as fish oil and garlic can increase the risk of bleeding in people taking warfarin (Coumadin) or aspirin, or blood-thinning supplements such as ginkgo, policosanol, and high-dose vitamin E.
Also be aware that some supplements may also interfere with laboratory tests, particularly high doses of biotin(often found in hair and nail supplements). Vitamin C at doses of 250 mg or more may interfere with certain kinds of stool tests, while calcium supplements (at any dose) may interfere with bone mineral density scans if taken within 24 hours of the scan.
You can learn more about the potential interactions of supplements with drugs in the “Concerns and Cautions” section of each of our product reviews.
© Copyright WLL, INC. 2022. This blog provides healthcare tips and advice that you can trust about a wide variety of general health information only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment from your regular physician. If you are concerned about your health, take what you learn from this blog and meet with your personal doctor to discuss your concerns.