Many people think that taking a daily cocktail of vitamins, minerals, antioxidants and other supplements is a prescription for a healthy diet. But it’s also likely that they don’t know whether the nutrients they’re taking are fat soluble, water soluble, or if they are getting more of some nutrients than they need.
Supplements, in general, are viewed as good for you, and people may think, “If one is good, then more is probably better.” But that’s not necessarily true.
Getting too many fat- or water-soluble nutrients, either from the food you eat or from supplements, can be dangerous. Vitamin and mineral supplements are serious business, and taking more than you need – unless you are under the care of your doctor – may be bad for your health.
The Dangers of Too Much Anything
Taking a vitamin or supplement as directed on the package label is considered to be safe, but not following directions can lead to problems.
“Excesses of all nutrients, from water, to iron, to water-soluble B vitamins, can potentially cause toxicities,” says Norman Hord, PhD, MPH, RD, associate professor in the department of Food Science and Human Nutrition at Michigan State University. People who take vitamins and minerals in amounts above the established upper limits of the Dietary Reference Intakes (DRIs) may harm tissues where the vitamin is stored in their body, Hord explains. That’s why you shouldn’t take more than the recommended amount.
Vitamins and other nutrients play essential roles in maintaining good health, but they need to be consumed in the proper amounts. Vitamins are classified into two types: water-soluble and fat-soluble vitamins. They are divided into these groups according to how they are dissolved and stored in your body. Fat-soluble vitamins reside in your body’s fatty tissue and liver and are used as needed by your body. By contrast, water-soluble vitamins dissolve in water and generally are not stored in your body.
Water-Soluble Vitamins and Nutrients
Because water-soluble vitamins and nutrients dissolve in water, the continuous supply your body needs calls for a steady daily intake, from the foods you eat, from the supplements you take, or from a combination of foods and supplements. Vitamins C, B12, thiamin, niacin, riboflavin, tryptophan, pantothenic acid, biotin, and folic acid are all classified in the water-soluble category.
Water-soluble nutrients work best when you get them in the proper amounts. When you eat or take more than your body needs, the body adapts by absorbing just what it needs, and then it usually excretes the excess in your urine – but not always. A study in the August 2010 Journal of Nutrition Science and Vitaminology found that urinary excretion of certain vitamins and other nutrients was reduced when study participants fasted.
The field of nutrition is ever-changing, and experts used to think that taking excess amounts of a water-soluble nutrient was harmless because the excesses would just be eliminated in urine. Today, we know that’s not the case, and that some water-soluble vitamins and nutrients are handled differently by the body than others.
Just because most water-soluble vitamins are not stored by the body, you can’t assume that it is safe or effective to take more than the safe upper limit. In addition, you need to account for the vitamins and nutrients you get from the food you eat, says Ruth Frechman, MS, RD, a spokesperson for the American Dietetic Association.
“Certain water-soluble vitamins in excess can cause problems, such as too much vitamin B6 can cause nerve problems, too much niacin can cause flushing, and excess vitamin C can cause kidney stones,” Frechman observes. Excess folic acid may also mask a vitamin B12 deficiency, which is more common in people over age 50.
Vitamins A, D, E, and K are the fat-soluble vitamins. Unlike water-soluble vitamins, these vitamins dissolve in fat and are stored in body tissues. Because they are stored, over time they can accumulate to dangerous levels and can lead to a condition called hypervitaminosis, meaning excess amounts of a vitamin in the body, if more than the recommended amount is taken.
“Too much vitamin A, D, or K can lead to increased levels that are unhealthy and can cause health consequences,” says Frechman. She adds that too much vitamin A can lead to birth defects, and too high levels of vitamin E may increase the risk of hemorrhaging. Excess vitamin K can lessen or reverse the effect of blood thinner medicines and prevent normal blood clotting.
Vitamin D has been one of the more controversial vitamins. Even though it is a fat-soluble vitamin, it appears to be tolerated in the body at higher levels.
As of 2010, the Institute of Medicine recommends a daily allowance of 600 international units (IU) of vitamin D for everyone ages 1 to 70, with an upper limit of 4,000 IU for those ages 9 and older.
Some experts, like vitamin D researcher and Creighton University professor Robert Heaney, MD, think the upper limit levels are still not set high enough and that more vitamin D may be necessary to foster good health. “The new upper limit for vitamin D has been doubled to 4,000 IU per day, which will meet the needs of most healthy people, but the research shows the toxic level is much higher than the established ceiling,” Heaney tells WebMD.
Frechman points out that vitamin D is also a hormone, which makes it unique in its properties. This dual function may explain why it functions differently than the other fat-soluble vitamins and renders it less harmful at higher intakes.
Too Much Can Cause Harm
Exceeding the government set tolerable upper limits can be a problem. “There is a reason for the tolerable upper limits that needs to be respected. Research has shown at which levels nutrients can cause potential problems, and these numbers take into account all sources of vitamins and minerals from food, fortified food and supplements,” says Frechman.
When the level goes beyond the safe upper limits, vitamins can act like drugs, says Roberta Anding, MS, RD, spokesperson for the American Dietetic Association, director of sports nutrition at Texas Children’s Hospital, and dietitian for the Houston Texans pro football team. Excessive calcium intake, more than 2,500 mg a day, can interfere with kidney function, cause kidney stones and constipation, and interfere with the absorption of iron and zinc.
The Risks of Fortified Foods Combined With Supplements
Fortified foods are another way people get additional nutrients. Historically, fortified foods were the way Americans filled some nutrient voids. Public health concerns over nutrient deficiencies led to production practices like adding iodine to salt, grains enriched with B vitamins and iron, and milk fortified with vitamins A and D.
But the combination of whole foods, supplements, and fortified foods raises safety concerns with experts. Eating fortified foods while also taking supplements can cause a person’s diet to exceed safe upper levels and potentially lead to a toxic buildup.
Six Brazil nuts, which weigh about 1 ounce, contain 544 micrograms of selenium, says Frechman. That’s a whopping 780% of the Daily Value of this trace mineral, which is only needed in small amounts.
The bottom line to remember is that if you are taking supplements, know the tolerable upper limit of the vitamins and minerals you’re taking, and check all labels to make sure your food choices are not enriched with the same nutrients. Your best option is to consult a doctor or dietitian before you begin taking any supplement.