Research Tips

May 5, 2009
If the label of a food or dietary supplement indicates 100% of the "Daily Value" for vitamin A, then one serving of the product contains about 200% of the daily intake currently recommended by the Institute of Medicine. Since high vitamin A intake may promote bone loss and birth defects, revision of labeling regulations is long overdue.
Nutr Rev. 2007 Oct;65(10):425-38.


May 11, 2009
Less than 2 milligrams of vitamin B-6 is all that is needed to meet an adult’s daily needs; only 200 milligrams consumed daily can cause nerve damage over time. Check that your dietary supplement does not contain toxic levels of this essential nutrient.
Ned Tijdschr Geneeskd. 2005 Nov 12;149(46):2545-6.


July 14, 2009
Adequate calcium is good for bone health, but it is possible to get too much. The Institute of Medicine considers 2500 mg/day to be the upper limit. Indiscriminate use of calcium- fortified foods plus supplements can easily go over that limit.
ODS Dietary Supplement Fact Sheet: Calcium


July 24, 2009
Vitamin B-6 is needed to make blood, keep the nervous and immune systems functioning properly, and regulate blood glucose levels. But, high doses of this vitamin can damage nerves - especially those in the arms, hands, legs and feet.
Institute of Medicine DRI Chapter on Vitamin B-6


August 6, 2009
It is important to consume adequate amounts of all essential nutrients. However, because excessive intake of some nutrients can be harmful, a “Tolerable Upper Intake Level” has been established for many nutrients. These values represent the maximum daily amount of a nutrient thought to not cause harm.
Establishing Upper Intake Levels for Nutrients


September 5, 2009
Vitamin B-6 is required in tiny amounts measured in thousandths of a gram. Many foods contain vitamin B-6, so it is unlikely to be too low unless your diet is extremely limited in variety or total food consumed. B-6 supplements in high doses, however, can cause nerve damage.
Ned Tijdschr Geneeskd. 2005 Nov 12;149(46):2545-6.


October 13, 2009
Fiber can help to prevent constipation. Excessively high fiber intake, however, can interfere with essential mineral absorption and can even cause constipation if inadequate fluids are consumed.
Nutr Rev. 2002 May;60(5 Pt 1):127-34.


December 22, 2009
High-fat meals may increase the risk of a heart attack for several hours because arteries narrow and blood flow slows. Enjoy the higher fat holiday foods, but in moderation.
Am J Cardiol. 1997 Feb 1;79(3):350-354


April 8, 2010
The theory that heart disease is caused by too much iron in the body has been refuted by a number of studies. Too much iron is mainly a concern for those with the genetic condition called hemochromatosis.
Can J Cardiovasc Nurs. 2009;19(1):26-32.


August 10, 2010
Foods and food components that show potential for preventing cancer are not necessarily beneficial during the treatment of cancer. A review of clinical trials reported that supplementation with vitamins C and E and beta carotene should not be used during chemotherapy.
J Natl Cancer Inst. 2008 Jun 4;100(11):773-83.


August 24, 2010
Too much of a good thing can be bad. This applies to nutrients and even exercise. “Tolerable Upper Intake Levels” have been established for many nutrients to help people know how much is too much.
Proc Nutr Soc. 2003 May;62(2):413-20.


September 22, 2010
Vitamin A is needed for normal growth, reproduction, bone health, blood cell production, skin health and immune function, but too much vitamin A (just 2 to 3 times the current recommended vitamin A intake) has been linked to increased bone loss and birth defects.
Nutr Rev. 2007 Oct;65(10):425-38.


March 9, 2011
An old medical condition called "milk alkali syndrome" has resurfaced and researchers are recommending a new name: "calcium alkali syndrome." Overuse of calcium supplements and calcium-containing antacids can cause high blood pressure and even kidney failure. Researchers recommend keeping total calcium intake below 1200 to 1500 mg per day.
BMJ. 2007 August 25; 335(7616): 397–398.


July 7, 2011
Over time, excess consumption of fat and sugar have been found to lead to increased rates of cell death in organs like the liver and kidneys. This is thought to be a key factor in the development of conditions like type 2 diabetes. New research is finding that 3 specific small RNA molecules increase in the lipid overload condition and cause cell death.
Cell Metab. 2011 Jul 6;14(1):33-44.


July 15, 2011
It is difficult to drink too much water, but it is possible. The Institute of Medicine points out that the maximal adult kidney excretion rate is 0.7 to 1.0 liters of water per hour. Unless the rate of sweat loss is substantial, consuming water at or above this rate could be harmful and even deadly.
Institute of Medicine, Dietary Reference Intakes for Water


March 27, 2012
Using a human cell culture technique, researchers found that some antioxidants such as resveratrol and genistein can damage DNA. This may prove to be another example of the "dose making the poison" since moderate intake of these antioxidants from foods seems to protect DNA from damage.
PNAS, 2012; DOI: 10.1073/pnas.1114278109


March 3, 2013
Although meeting essential nutrient needs during pregnancy is needed for optimal infant health, excessive intake of a nutrient also may cause problems. A recent study found that infants with high blood levels of vitamin D at birth were more likely to develop allergies within their first 2 years of life.
Allergy. 2013 Feb;68(2):220-8.


June 5, 2013
Tea is a source of fluoride in the diet that may benefit dental and bone health. However, proving that too much of a good thing can be bad for you, a woman who consumed very large amounts of concentrated tea for about 20 years suffered from fluoride toxicity that was serious enough to cause her to lose her teeth.
N Engl J Med 2013;368:1140.


January 31, 2014
Supplementation of adult men with vitamin D2 (3800 IU/day) for 6 weeks caused an increase in blood markers of muscle damage. Based on this study, high dose supplementation with vitamin D may have detrimental effects in athletes.
Nutrients. 2013 Dec 20;6(1):63-75.


February 2, 2014
Too much of a good thing can be bad. A new study found that feeding mice supplemental amounts of the antioxidants N-acetylcysteine (NAC) and vitamin E markedly increased tumor progression and reduced survival. This result is similar to the effects seen in smokers taking beta-carotene supplements.
Sci Transl Med. 2014;6(221):221ra15.


February 22, 2014
Consuming adequate amounts of folic acid is important to overall health. However, taking high dose folic acid supplements can interfere with the timely diagnosis of vitamin B-12 deficiency that is common in older people and strict vegetarians.
Nutr Rev. 2004 Jun;62(6 Pt 2):S3-12.


May 27, 2014
Studies in mice show that supplementing the diet with the alpha-tochopherol form of vitamin E improves lung function, but the gamma-form worsens lung function. A newly published study of over 4500 people followed for 20 years found a similar relationship in humans. Other studies have found health benefits associated with both the alpha and gamma forms of vitamin E. Therefore Including a variety of vegetable oils in the diet is likely the best option to maintain a balanced intake of the various forms of vitamin E.
Respir Res. 2014 Mar 15;15:31.


January 17, 2015
Tanning Beds and Vitamin D: It generally is assumed that sun exposure cannot lead to excessive vitamin D levels in the body. However, a recent case study of a white woman indicated that her excessively high blood level of vitamin D (hypervitaminosis D) was caused by tanning bed use three to four times a week. When she ceased using the tanning bed, her blood level of vitamin D (25-hydroxyvitamin D) returned to a normal level within a month.
Ann Intern Med. 2014 Jun 3;160(11):810-1.


February 16, 2015
Folic Acid Excess: A study conducted with rats found that high folic acid intake (20 times recommended intake) before, during, and after pregnancy caused their babies to become overweight and insulin resistant in adulthood. This effect was more pronounced in female offspring. How this may translate to humans is not clear, but it supports heeding the U.S. folic acid tolerable upper intake level that is about twice the RDA.
J Endocrinol. 2015 Mar;224(3):245-59.


July 17, 2015
Drinking During Exercise: When people drink too much during very long endurance events, they can dangerously lower their blood sodium level - a condition called hyponatremia. A new consensus statement cautions athletes against drinking before they are thirsty and recommends using thirst as their guide to drink during long bouts of exercise. However, it should be recognized that waiting for thirst can lead to dangerous dehydration in hot and humid situations in which the rate of water loss in sweat can exceed the rate at which water can be absorbed by the intestine.
Clin J Sport Med. 2015 Jul;25(4):303-20.


July 25, 2015
Vitamin B-6 is needed to make blood, keep the nervous and immune systems functioning properly, and regulate blood glucose levels. But, high doses of this vitamin can damage nerves - especially those in the arms, hands, legs and feet.
Institute of Medicine DRI Chapter on Vitamin B-6


August 8, 2015
Essential Nutrients and Balance: It is important to consume adequate amounts of all essential nutrients. However, because excessive intake of some nutrients can be harmful, a “Tolerable Upper Intake Level” has been established for many nutrients. These values represent the maximum daily amount of a nutrient thought to not cause harm.
Establishing Upper Intake Levels for Nutrients


October 16, 2015
Oxidative Stress and Cancer: A new study indicates that the cancer cells that spread cancer throughout the body by metastasis are less likely to survive when exposed to oxidative stress. Consequently, researchers think that consuming large amounts of antioxidants from the diet and/or supplements may actually promote the spread of cancer. Again, too much of a good thing is not good.
Nature. 14 October 2015. [Epub ahead of print]


January 24, 2016
Potential Selenium Toxicity in Nuts: Brazil nuts are an excellent source of selenium. However, moderation is the key since only five nuts a day can contain more selenium than the tolerable upper intake level established by the Institute of Medicine.
Chemosphere. 1995 Feb;30(4):801-2.


September 27, 2016
Zinc and Infection: All essential nutrients are part of a balancing act. Too little and too much of a nutrient are both potentially bad. A new study, using a mouse model, found that high zinc intake altered the lower intestinal bacterial ecology in a way that favored the development of the bacterium Clostridium difficile. This bacteria can cause infections that are highly resistant to treatment.
Nature Medicine. 2016 18 January. [Epub ahead of print]


October 18, 2016
Folic Acid Excess and Vitamin B12 Function: High folic acid intake has been associated with neurological damage when vitamin B12 status is low. A new study found that people with a fairly common gene alteration for a vitamin B-12 transport protein are much more likely to develop peripheral neuropathy, especially when folic acid intake is high.
Am J Clin Nutr. 2016 Oct 12. [Epub ahead of print]


September 25, 2017
Excess Dietary Manganese and the Heart: Manganese is an essential nutrient that is found in many "healthy" foods." However, it is possible to exceed the "tolerable upper intake level" of manganese when foods that are rich in the mineral make up a large part of the diet. Excess manganese is known to affect the brain with a Parkinson's disease-like condition. Now, a new study with mice found that high dietary manganese levels altered immune function to allow the pathogenic bacterium Staphylococcus aureus to infect the heart. How this might relate to humans is currently unknown.
Cell Host & Microbe. 21 September 2017. [Epub ahead of print]


October 7, 2017
Excess Nutrients: Too much of a good thing isn’t always good. For example, high intake of calcium and vitamin D increased the risk of poor cognitive function in elderly.
Nutr Res. 2008 May;28(5):285-92.


August 14, 2018
Pantothenic Acid Toxicity: No tolerable upper intake level has been established for pantothenic acid (vitamin B5) due to its apparent safety within a wide range of intakes. However, very high doses of pantothenic acid supplements (such as 10,000 mg per day) have caused upset stomach and diarrhea. Excess intake from food sources has not been reported and is highly unlikely.
Linus Pauling Institute » Micronutrient Information Center - Pantothenic-acid


August 17, 2018
Calcium Excess: The Tolerable Upper Intake Level for calcium, established by the Institute of Medicine in 2010, is 2500 mg/day for adults 19-50 years of age and 2000 mg/day for adults 51 years and older. Since these values were established, additional research related to risks of prostate cancer suggests that it may be best to limit calcium intake (from food and supplements combined) to 1000 to 1200 mg/day.
Linus Pauling Institute » Micronutrient Information Center - Calcium


August 24, 2018
Potassium Excess: a tolerable upper intake for potassium was not set by The Food and Nutrition Board of the Institute of Medicine because adverse effects from high dietary potassium has not been documented in healthy individuals. Those in individuals with kidney problems or those consuming excessive potassium supplements can have serious gastrointestinal problems, muscle problems and abnormal heart rhythm.
Linus Pauling Institute » Micronutrient Information Center - Potassium


August 31, 2018
Vitamin A Toxicity: Besides being an essential nutrient, vitamin A can also be consumed in excess, causing dizziness, headaches, nausea, skin irritation, joint pains and bones, coma, and can cause congenital birth defects. Vitamin A can accumulate in the liver with high levels of liver consumption but most excessive vitamin A comes from dietary supplements.
Linus Pauling Institute » Micronutrient Information Center - Vitamin-A


September 7, 2018
Excess Vitamin C: Excess vitamin C from supplements can cause diarrhea in some individuals, but generally excess vitamin C is excreted by the body in urine. When people have been taking more than 1000 mg vitamin C daily, it is important to slowly decrease the dose over time to prevent what is called rebound scurvy.
Linus Pauling Institute » Micronutrient Information Center - vitamin-C


September 14, 2018
Excess Vitamin B1: No toxic effects from excess thiamin in food or dietary supplements (up to 200 mg/day) have been recorded. Large intravenous doses of B1 have caused life-threatening anaphylactic reactions in a few individuals. There is no established Tolerable Upper Intake Level for thiamin, however, the Expert Group on Vitamins and Minerals of the Food Standards Agency, United Kingdom recommends not to exceed 100 mg per day from dietary supplements.
Linus Pauling Institute » Micronutrient Information Center - Thiamin


September 16, 2018
Essential Nutrients and Normal Growth: During pregnancy, good nourishment of a woman's body provides an adequate supply of nutrients to the developing fetus and supports milk production after birth to meet the baby's needs. Poor nutrition of the mother can impair normal development in ways that are irreversible and can have serious adverse effects that persist even into adult life.
Nutr Rev. 2011 Nov;69 Suppl 1:S3-16.


September 19, 2018
Chromium Excess: The toxicity of chromium is relatively low compared to recommended intake levels. No Tolerable Upper Intake Level has been established by the Institute of Medicine. However, the Expert Group on Vitamins and Minerals in the United Kingdom provided an adult "Guidance Level" of no more than 10 mg per day from dietary supplements.
Safe Upper Levels for Vitamins and Minerals, 2003, pp. 172-179.


September 28, 2018
Riboflavin Excess: The toxicity of riboflavin (vitamin B2) is very low and no Tolerable Upper Intake Level has been established by the Institute of Medicine. The Expert Group on Vitamins and Minerals in the United Kingdom provide an adult "Guidance Level" of no more than 40 mg per day from dietary supplements.
SafeUpper Levels for Vitamins and Minerals, 2003, pp. 172-179.


October 5, 2018
Iron Excess: The Tolerable Upper Intake level for iron is set at 45 mg/day because doses much higher than this can cause gastrointestinal irritation and related symptoms. People with a hereditary condition called hemochromatosis can accumulate excessive amounts of iron over time due to a lack of the normal regulation of iron absorption that protects most people from iron overload.
Linus Pauling Institute » Micronutrient Information Center - Iron


October 19, 2018
Copper Excess: The adult RDA for copper is just under one mg per day and the Tolerable Upper Intake Level is 10 mg per day. Although consuming copper at this level is uncommon, there is some concern that 10 mg/day might be too high because of some evidence that men consuming 7.8 mg/day of copper for 147 days experienced some adverse changes in measures of immune function and antioxidant status.
Linus Pauling Institute » Micronutrient Information Center - Copper