Editing Multivitamin (section)

== Precautions ==
[[File:Bell curve of intake versus health effect.svg|210px|right]]
The amounts of each vitamin type in multivitamin formulations are generally adapted to correlate with what is believed to result in optimal health effects in large population groups. However, these standard amounts may not correlate with what is optimal in certain subpopulations, such as in children, pregnant women and people with certain medical conditions and medication.

The health benefit of vitamins generally follows a biphasic [[Dose-response relationship|dose-response curve]], taking the shape of a [[Gaussian function|bell curve]], with the area in the middle being the safe-intake range and the edges representing deficiency and [[toxicity]].<ref>{{cite book |vauthors=Combs GF |date=1998 |title=The vitamins: Fundamental aspects in nutrition and health. |publisher=Academic Press |location=San Diego, CA }}</ref> For example, the [[Food and Drug Administration]] recommends that adults on a 2,000 calorie diet get between 60 and 90 milligrams of vitamin C per day.<ref>{{cite web |url=http://www.crnusa.org/about_recs4.html |title=Vitamin and Mineral Recommendations|publisher=Council for Responsible Nutrition |access-date=2017-10-01 |url-status=dead |archive-url=https://web.archive.org/web/20121031115637/http://www.crnusa.org/about_recs4.html |archive-date=2012-10-31 }}. Retrieved 2011-03-30.</ref> This is the middle of the bell curve. The upper limit is 2,000 milligrams per day for adults, which is considered potentially dangerous.<ref>{{cite web|url=https://www.nlm.nih.gov/medlineplus/druginfo/natural/1001.html|date=2010|title=Vitamin C (Ascorbic acid)|website=MedlinePlus|publisher=U.S. National Library of Medicine|access-date=23 March 2018|archive-date=5 October 2015|archive-url=https://web.archive.org/web/20151005065616/https://www.nlm.nih.gov/medlineplus/druginfo/natural/1001.html|url-status=live}}</ref>

In particular, pregnant women should consult their doctors before taking any multivitamins. For example, either an excess or deficiency of [[vitamin A]] can cause birth defects.<ref>{{cite journal | vauthors = Collins MD, Mao GE | title = Teratology of retinoids | journal = Annual Review of Pharmacology and Toxicology | volume = 39 | pages = 399–430 | year = 1999 | pmid = 10331090 | doi = 10.1146/annurev.pharmtox.39.1.399 }}</ref>

Long-term use of [[beta-carotene]], vitamin A, and [[vitamin E]] supplements may shorten life,<ref name=":Bjelakovic2012" /> and increase the risk of lung cancer in people who smoke (especially those smoking more than 20 cigarettes per day), former smokers, people exposed to asbestos, and those who use alcohol.<ref>{{Cite web |title=Beta-Carotene |website=MedlinePlus |publisher=U.S. National Library of Medicine |date=1 November 2017 |access-date=6 October 2019 |url=https://medlineplus.gov/druginfo/natural/999.html |archive-date=26 December 2016 |archive-url=https://web.archive.org/web/20161226150215/https://medlineplus.gov/druginfo/natural/999.html |url-status=live }}</ref> Many common brand supplements in the [[United States]] contain levels above the [[Dietary Reference Intake|DRI]]/RDA amounts for some vitamins or minerals.

Severe vitamin and mineral deficiencies require medical treatment and can be very difficult to treat with common over-the-counter multivitamins. In such situations, special vitamin or mineral forms with much higher potencies are available, either as individual components or as specialized formulations.

Multivitamins in large quantities may pose a risk of an acute [[overdose]] due to the toxicity of some components, principally [[Iron poisoning|iron]]. However, in contrast to iron tablets, which can be lethal to children,<ref>{{cite journal | vauthors = Cheney K, Gumbiner C, Benson B, Tenenbein M | title = Survival after a severe iron poisoning treated with intermittent infusions of deferoxamine | journal = Journal of Toxicology. Clinical Toxicology | volume = 33 | issue = 1 | pages = 61–66 | year = 1995 | pmid = 7837315 | doi = 10.3109/15563659509020217 }}</ref> toxicity from overdoses of multivitamins are very rare.<ref>{{cite journal | vauthors = Linakis JG, Lacouture PG, Woolf A | title = Iron absorption from chewable vitamins with iron versus iron tablets: implications for toxicity | journal = Pediatric Emergency Care | volume = 8 | issue = 6 | pages = 321–324 | date = December 1992 | pmid = 1454637 | doi = 10.1097/00006565-199212000-00003 | s2cid = 19636488 }}</ref> There appears to be little risk to supplement users of experiencing acute side effects due to excessive intakes of micronutrients.<ref>{{cite journal | vauthors = Kiely M, Flynn A, Harrington KE, Robson PJ, O'Connor N, Hannon EM, O'Brien MM, Bell S, Strain JJ | title = The efficacy and safety of nutritional supplement use in a representative sample of adults in the North/South Ireland Food Consumption Survey | journal = Public Health Nutrition | volume = 4 | issue = 5A | pages = 1089–1097 | date = October 2001 | pmid = 11820922 | doi = 10.1079/PHN2001190 | doi-access = free }}</ref> There also are strict limits on the retinol content for vitamin A during pregnancies that are specifically addressed by prenatal formulas.

As noted in dietary guidelines from Harvard School of Public Health in 2008, multivitamins should not replace healthy eating or make up for unhealthy eating.<ref>Harvard School of Public Health (2008). Food pyramids: What should you really eat?. Retrieved from http://www.hsph.harvard.edu/nutritionsource {{Webarchive|url=https://web.archive.org/web/20110420002404/http://www.hsph.harvard.edu/nutritionsource/ |date=2011-04-20 }}</ref>{{failed verification|date=August 2015}} In 2015, the [[United States Preventive Services Task Force|U.S. Preventive Services Task Force]] analyzed studies that included data for about 450,000 people. The analysis found no clear evidence that multivitamins prevent cancer or heart disease, helped people live longer, or "made them healthier in any way."<ref>{{Cite web|title=Why You Don't Need A Multivitamin – Consumer Reports|url=http://www.consumerreports.org/cro/news/2015/05/why-you-don-t-need-a-multivitamin/index.htm|access-date=2015-09-10|archive-date=2015-09-10|archive-url=https://web.archive.org/web/20150910141810/http://www.consumerreports.org/cro/news/2015/05/why-you-don-t-need-a-multivitamin/index.htm|url-status=live}}</ref>