Multivitamin bashing seems to be in season. The March 2008 Harvard Men’s Health Watch (1)gives the impression that few of the ingredients in a multivitamin are worth taking. The June 2008 Nutrition Action Health Letter (2) suggests taking a multivitamin every other day instead of every day. The central concern of both articles is folic acid—specifically,getting too much folic acid.
Here’s better advice: Take a standard multivitamin every day, but stay away from heavily fortified foods that deliver a full day’s dose—or sometimes more—of folic acid (see “Folic Acid in Fortified Foods“). This will provide reasonable amounts of many essential nutrients without going overboard on folic acid.
Folate and Folic Acid
Folate and folic acid are members of the B vitamin family. Their names come from folium,the Latin word for leaf. Folate is the form found naturally in fruits, vegetables, grains, and other foods. Folic acid is the synthetic form that is added to food or used as an ingredient in vitamin supplements. The body absorbs folic acid faster than it absorbs folate, but then must convert it into folate before it can get to work.
Folate’s job involves shuttling single carbon atoms and their attached hydrogens and oxygens from one chemical compound to another.That tiny transfer makes folate a key player in essential cell functions. It helps make, protect, and repair DNA, the double helix that carries the body’s operating manual. It also helps convert some amino acids (the building blocks of proteins) into others. Good sources of natural folate include beans, various greens, sunflower seeds, and many other fruits and vegetables (see”Natural Folate in Foods“).
Since 1998, folic acid has been added to most enriched bread flours, cornmeal, pasta, rice, and other grain products in the U.S. and Canada. This was done to help prevent spina bifida and anencephaly, two birth defects that are caused in part by too little folate in a mother’s body around the time her baby is conceived.This program has increased average folic acid intakes by about 100 micrograms a day (3) and has decreased the number of American children born with a neural tube defect by 25% to 50%. (4) The overall evidence from controlled trials shows that extra folic acid also helps protect against stroke (5), and many studies suggest it probably reduces the risk of heart disease, too. (6)
|Lentils,½ cup cooked||180|
|Spinach,½ cup cooked||132|
|Black beans, ½ cup cooked||128|
|Sunflower seeds, 1½ ounces||101|
|Turnip greens, ½ cup cooked||85|
|Broccoli,½ cup cooked||84|
|Orange juice, 1 cup fresh squeezed||74|
Source: USDA National Nutrient Database
The Institute of Medicine, which is charged with setting healthy and safe intakes of vitamins and other nutrients, recommends that most adults get 400 micrograms of folate/folic acid a day, and 600micrograms a day for pregnant women. (7) The Institute recommends against getting more than 1,000 micrograms per day of folic acid from supplements or fortified food; folate intake from food is not a concern.
One main reason for the upper limit on folic acid is that getting too much folic acid can mask the signs of a vitamin B12 deficiency. Although this isn’t common in the general population, up to 1 in 6older people either don’t get enough vitamin B12 or don’t absorb it efficiently. Too much folic acid can hide the signs of anemia, an early warning of a vitamin B12 deficiency. This could allow the problem to progress to the point of causing confusion, dementia, and/or severe and irreversible damage to the nervous system.
There are other concerns, too. “Normal” amounts of folic acid can inhibit the origination, growth, and progression of early tumors. But the possibility exists that too much folic acid can accelerate the growth of existing tumors. A few studies have suggested that excess folic acid may—and we stress the “may” here—be associated with increased risk for colorectal (8, 9), breast (10), and prostate (11)cancers. Although these studies are limited, and other, similar studies have shown no association between folic acid and increased cancer risk, they sound a warning about getting too much folic acid that deserves further investigation.
Did You Know…
The % Daily Value (%DV) for folate is 400 micrograms. So if a food contains 50% of the Daily Value for folate, it contains 200 micrograms of folate.
For example, one highly publicized study suggested that folic acid fortification might have caused a small increase in the incidence of colon cancer. (8) There’s another equally plausible explanation for the increase—greater detection of existing tumors in the colon and rectum due to more widespread use of colonoscopy. The steady decline in deaths from colon cancer before and after the onset of folic acid fortification suggests that screening, not folic acid fortification, is responsible for the uptick in colon cancer rates (view a graph from this colon cancer study (8) that shows this trend). The overall evidence from studies in humans shows a lower risk of colon and breast cancer with greater intake of folate or folic acid,rather than an increased risk. (12-15)
At a high intake, the body can’t process all the folic acid into folate. It is possible that unconverted folic acid circulating in the bloodstream could elbow aside folate for spots inside binding enzymes, carrier proteins, and binding proteins. (16) In theory, this could decrease the amount of folate carried into brain and other tissues—like dying of starvation in a land of plenty. In practice, though, whether this is a real problem is not clear.
Too Much of a Good Thing?
Too much folate from food isn’t an issue. It comes naturally packaged in balance with other micronutrients, and the body regulates its absorption. Folic acid added to food is a different story. Some breakfast cereals, nutrition bars, and other fortified foods deliver up to 800 micrograms of folic acid, and that’s about double the recommended daily dose. The Institute of Medicine’s upper limit is 1,000 micrograms of folic acid from fortified foods a day.
If you’ve ever had a sunburn or post-sundae bellyache, you know that it’s possible to get too much of a good thing. This applies to vitamins and minerals. Too much retinol (also known as preformed vitamin A), for example, is one such case—it can weaken bones and lead to fractures. (17) Too much folic acid, especially when it is unbalanced by other micronutrients, may be another case. In unfortified foods, folate comes with a host of other vitamins, minerals, and as-yet undiscovered phytonutrients that almost certainly work together. In fortified foods and single supplements, it may be working alone. That’s why it’s best to get your nutrients from food.
Sometimes, though, food doesn’t supply enough vitamins and minerals. Fortified foods can help correct deficiencies, but they can overdo one nutrient, which may counteract the benefit. Multivitamin-multimineral supplements can’t replace food—nothing can. But they offer as balanced a combination of vitamins and minerals as the evidence currently allows, without megadoses. The precise role that these supplements play in good health is still up in the air, but we believe that they offer definite benefits for some people and good nutritional “insurance.” (See “Nutrition Insurance Policy” to learn more about why we recommend taking a daily multivitamin.)
Rather than giving up a dailymultivitamin-multimineral supplement or taking it every other day as a way to prevent getting too much folic acid, a better strategy would be to get in the habit of taking a multivitamin-multimineral supplement every day and avoiding foods fortified with more than 100-200 micrograms of folic acid (25% to 50% of the % Daily Value). We will continue to monitor the evidence as it emerges, particularly from long term studies, to fine tune guidance about the optimal intakes of folic acid, vitaminB12, and other nutrients.
1.Multivitamins and your health: A reappraisal. (Cover story). Harvard Men’s Health Watch. 2008; 12:1-4.
2.Liebman B, Schardt D. Picking a Multivitamin Gets Tricky. (Cover story). Nutrition Action Health Letter. 2008; 35:1-4.
3.Bentley TG, Willett WC, Weinstein MC, Kuntz KM. Population-level changes in folate intake by age, gender, and race/ethnicity after folic acid fortification. American Journal of Public Health. 2006; 96:2040-7.
4.Mills JL, Signore C. Neural tube defect rates before and after food fortification with folic acid. Birth Defects Res A Clin Mol Teratol. 2004; 70:844-5.
5.Wang X, Qin X, Demirtas H, et al. Efficacy of folic acid supplementation in stroke prevention: a meta-analysis. Lancet. 2007; 369:1876-82.
6.Moens AL, Vrints CJ, Claeys MJ, Timmermans JP, Champion HC, Kass DA. Mechanisms and potential therapeutic targets for folic acid in cardiovascular disease. Am J Physiol Heart Circ Physiol. 2008; 294:H1971-7.
7.Institute of Medicine. Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. Washington, DC: National Academy Press, 1999.
8.Mason JB, Dickstein A, Jacques PF, et al. A temporal association between folic acid fortification and an increase in colorectal cancer rates may be illuminating important biological principles: a hypothesis. Cancer Epidemiology, Biomarkers and Prevention. 2007; 16:1325-9.
9.Cole BF, Baron JA, Sandler RS, et al. Folic acid for the prevention of colorectal adenomas: a randomized clinical trial. JAMA. 2007; 297:2351-9.
10.Lin J, Lee IM, Cook NR, et al. Plasma folate, vitamin B-6, vitamin B-12, and risk of breast cancer in women. American Journal of Clinical Nutrition. 2008; 87:734-43.
11.Stevens VL, Rodriguez C, Pavluck AL, McCullough ML, Thun MJ, Calle EE. Folate nutrition and prostate cancer incidence in a large cohort of US men. American Journal of Epidemiology. 2006; 163:989-96.
12.Giovannucci E, Stampfer MJ, Colditz GA, et al. Multivitamin use, folate, and colon cancer in women in the Nurses’ Health Study. Annals of Internal Medicine. 1998; 129:517-524.
13.Ericson U, Sonestedt E, Gullberg B, Olsson H, Wirfalt E. High folate intake is associated with lower breast cancer incidence in postmenopausal women in the Malmo Diet and Cancer cohort. American Journal of Clinical Nutrition. 2007; 86:434-43.
14.Sanjoaquin MA, Allen N, Couto E, Roddam AW, Key TJ. Folate intake and colorectal cancer risk: a meta-analytical approach. International Journal of Cancer. 2005; 113:825-8.
15.Pietro Ferrari MJTNAMNSAOATKOMKJM-CB-RFC-CSMSRJ. Lifetime and baseline alcohol intake and risk of colon and rectal cancers in the European prospective investigation into cancer and nutrition (EPIC). International Journal of Cancer. 2007; 121:2065-2072.
16.Smith AD, Kim YI, Refsum H. Is folic acid good for everyone? American Journal of Clinical Nutrition. 2008; 87:517-33.
17.Feskanich D, Singh V, Willett WC, Colditz GA. Vitamin A intake and hip fractures among postmenopausal women. JAMA. 2002; 287:47-54.
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