You might notice some supplements boast about double the recommended daily allowance (RDA) for certain nutrients. It may sound like such supplements can provide extra doses of health benefit because of this. But do you really need that much of each nutrient? What benefits can mega doses of certain nutrients provide?
The answer is not always clear for all people since nutrient needs differ from one person to the next. However, there is some research to suggest that some doses above the RDA may benefit health. Read below to learn about the nutrients you will commonly see in large doses and how such large doses can either benefit health or cause harm.
What is the RDA?
The RDA is the daily dosage of each vitamin and mineral needed to meet the nutrient needs of most healthy people (1). This set number is determined by the Food and Nutrition Board of the Institute of Medicine (IOM) and is based on a person’s sex, age, and unique physical condition (such as pregnancy).
The IOM is a non-profit organization with a set of independent experts that make policy recommendations like the RDAs (2). These RDAs can change every now and then depending on the status of scientific evidence.
With what nutrients can a larger dose provide health benefits?
With certain nutrients, taking a higher daily dose than the RDA can provide additional benefits. One such example is folate. Folate (Folic Acid) is a water-soluble B vitamin that for some people, is beneficial in amounts above the usual recommended daily allowance. The RDA of folate for most adults is 400 micrograms (3). However, if you have a history of a pregnancy with neural tube defects, then experts recommend taking 4000 micrograms daily for three months before you become pregnant to three months after you conceive to prevent neural tube defects (7).
And when it comes to other B vitamins, research shows that high doses of B vitamins in healthy adults can reduce inflammation and oxidative stress (8). By reducing inflammation, you may be able to lower your risk of developing chronic conditions like heart disease.
Regardless of the potential benefits, you should talk to your healthcare provider before taking high doses of any supplement. This is a precaution to be sure it will not interfere with your current healthcare plan.
The RDA for Vitamin C is about 75 to 90 milligrams daily (3). However, some research shows that taking up from 250 to 1000 milligrams daily may help reduce onset of cold virus symptoms in active individuals exposed to cold environments or extreme exercise (4). This large dose may also help those with low- normal vitamin C status like the elderly or smokers.
In the general population, it may help shorten duration of the cold (4). However, it’s unlikely to have any benefit once the cold has already started. Since vitamin C is a water-soluble vitamin, it will not store in the body, so higher doses will not accumulate in the body and cause any harm. However, taking more than the daily limit could cause symptoms such as diarrhea, abdominal pain, and nausea.
Another nutrient where higher doses may help improve your health is vitamin D. The RDA is 600 IUs for most adults (3). However, if you’re vitamin D deficient, your doctor may recommend mega doses of 2000 IUs of vitamin D3 daily or mega doses of vitamin D2 weekly to help boost your vitamin D to normal levels (5,6).
Once your vitamin D blood levels are within a normal range, a smaller dose daily will do. Having a normal level of vitamin D in the body can aid in calcium, bone, and muscle metabolism (5). The upper limit of vitamin D is around 10,000 to 40,000 IU daily, which can cause symptoms like weight loss, polyuria, and heart arrhythmias (6). Therefore, you should not consume within this upper limit range unless directed by a physician.
What vitamins and nutrients should I not take above the RDA?
One vitamin you should not take over the RDA is vitamin A. Although this vitamin, in moderation, can help support bone, vision, and immune system health, high doses can be harmful (2). The RDA for vitamin A for most adults is 700 to 900 micrograms or 2330 to 3000 IU daily (1).
Since Vitamin A is a fat-soluble vitamin, it stores itself in the liver (9). In excess, too much preformed vitamin A (not beta-carotene or other provitamin A carotenoids) can overwhelm the liver and cause symptoms like:
- Skin irritation
- Joint pain
- Liver damage
In pregnant women, vitamin A is important for fetal growth and development (10). However, too much preformed vitamin A intake or topical retinoid use in this population can lead to an increased risk of birth defects (9). Therefore, be sure to let your doctor know all medicines and supplements you’re taking to be sure you’re not taking too much of this or any other compound.
Vitamin E is another fat-soluble vitamin that can cause harm if too much is taken daily. In normal doses, vitamin E can benefit health through its antioxidant properties that can boost immune health (11). The recommended daily dosage for most adults is around 15 milligrams daily, and 19 milligrams daily for lactating women.
However, above this recommended dosage, vitamin E may cause side effects such as nausea, diarrhea, fatigue, weakness, rash, blurred vision, or intestinal cramping (12). More serious side effects of large doses of vitamin E may affect blood clotting in a way that could cause bleeding or hemorrhage in some people.
Another nutrient you should not take over the RDA is iron. The RDA of iron is 8 milligrams daily for most adults and 18 milligrams daily for menstruating women (1). Pregnant women may need around 27 milligrams daily to help support red blood cell and hemoglobin production for mom and baby (13).
Taking more than around 20 milligrams per kilogram of body weight of iron can cause gastrointestinal symptoms such as nausea, constipation, abdominal pain, vomiting, and faintness, especially if taken on an empty stomach (13). The only time where you may need to take a higher than RDA dose of iron is if your iron levels are low. In this case, a doctor may prescribe you a high dose iron supplement to take temporarily until your iron levels rise to normal levels.
Final note on taking more than the RDA
It may sound good that a supplement contains 500% or 1000% of a nutrient. More is better, right? This may be the case, but this is not always the case. Although some nutrients can benefit short-term health in larger doses, other nutrients should be kept at RDA doses for your own safety and benefit. If you have a question about a certain nutrient or compound that wasn’t mentioned here, then talk to your local pharmacist for guidance.
- Mayo Clinic (July 2009) “Mayo Clinic Women’s Healthsource Special Report: Vitamins and Minerals: What You Should Know About Essential Nutrients.”
- Michels, Ph.D., A. (March 31, 2016) “Why the Nutrition Facts Label Can Lead You Astray.” Oregon State University Linus Pauling Institute
- Health.gov (accessed March 14, 2020) “Appendix 7. Nutritional Goals For Age-Sex Groups Based on Dietary Reference Intakes andDietary Guidelines Recommendations.”
- National Institutes of Health Office of Dietary Supplements (last updated February 27, 2020)“Vitamin C.”
- National Institutes of Health Office of Dietary Supplements (last updated August 7, 2019)“Vitamin D.”
- Scragg, R. (May 2018) “Emerging Evidence of Thresholds for Beneficial Effects from Vitamin D Supplementation.”Nutrients, 10(5):561.
- March of Dimes (last reviewed February 2018) “Folic Acid Key Points.”
- Ford, T.C., et al. (December 2018) “The Effect of a High-Dose Vitamin B MultivitaminSupplement on the Relationship between Brain Metabolism and Blood Biomarkers of Oxidative Stress: A Randomized Control Trial.”Nutrients; 10(12):1860.
- National Institutes of Health Office of Dietary Supplements (updated February 14, 2020)“Vitamin A.”
- World Health Organization (accessed March 14, 2020) “Vitamin A supplementation during pregnancy.”
- National Institutes of Health Office of Dietary Supplements (updated February 28, 2020)“Vitamin E.”
- Mayo Clinic (October 18, 2017) “Vitamin E.”
- National Institutes of Health Office of Dietary Supplements (updated February 28, 2020) “Iron.”
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
Tell your doctor, pharmacist, and other healthcare providers about any dietary supplements and medicines you take. They can tell you if those dietary supplements might interact or interfere with your prescription or over-the-counter medicines or if the medicines might interfere with how your body absorbs, uses, or breaks down nutrients.