Too much of a good thing: How excessive vitamin and mineral use can harm you

Vitamins and minerals influence hundreds of biochemical processes that keep the body running. While it’s important to have adequate amounts, excess intake of these micronutrients can cause adverse health effects. Vitamins and minerals are essential to good health. They play a role in everything from normal vision, reproduction, metabolism, bone development, normal cell function and a healthy immune system. Since they’re so good for you, then more must be better, right? Especially if you want to get the full benefit from certain ones. Want stronger bones? Take lots of vitamin D, calcium and phosphorus. Want to blunt the rise in blood pressure caused by high intake? Load up on potassium. Want to boost your immune system? Pop vitamin E. Not so fast, warn medical and nutrition experts. It’s true, specific micronutrients influence particular biochemical processes, but taken in excess they can create their own set of problems.

When individuals believe they can prevent disease with mega-vitamins or mega-minerals, they put themselves at risk for toxicity. They believe the extra amounts help prevent disease, but at that level they don’t act as nutrients, they act as pharmacologic agents, explains an emeritus professor of medicine at the University of Toronto. Data from the American Association of Poison Control Centers (AAPCC) bears out the potential for harm. According to the AAPCC, in 2002 there were 9,630 poison exposures to pediatric multi-vitamin tablets. In addition, there were 2,789 poison exposures to vitamin A; 2,349 to vitamin C; 1,979 to vitamin E; 1,053 to copper and 119 to selenium.

What’s behind the numbers?

In all probability, the people who experienced problems with vitamins or mineral supplements wouldn’t have had any trouble if they’d focused on meeting their nutritional needs through a balanced diet.

Once you isolate a nutrient chemically, they take on a life of their own, whereas when they’re consumed as part of the food matrix, it limits that potential, says a director of nutritional sciences of Environ Health Sciences Institute, and former director of the Food and Nutrition Board at the Institute of Medicine. So just by eating a balanced diet, you’re likely to get all the nutrients you need without over-doing any one in particular. Take the mineral zinc for example. It promotes activity in about 100 enzymes and contributes to a healthy immune system, proper wound healing, and it helps maintain taste and smell. Zinc is found in very small quantities in a host of foods like red meat, poultry, beans, nuts, whole grain breads and dairy products. You pick up a little bit of it throughout the day just by eating a variety of foods. Most adult women need only about 8 milligrams per day; adult men need only 11 milligrams. Oysters have more zinc per serving than any other food, but you’d have to eat more than 50 to approach documented levels where health effects have been observed, and not just for one day. You’d probably have to consume that amount for an extended period before you experienced a problem like having it affect the amount of copper you absorb. However, medical case reports have cited severe nausea and vomiting within 30 minutes of taking mega-doses of zinc gluconate supplement.

In a few rare exceptions, foods containing very high quantities of certain micronutrients can cause acute illness. One of the most well-known is consumption of polar bear liver. For survival, artic explorers would kill and eat all the edible parts of these giants. But polar bear liver is chock full of vitamin A. One gram has astronomical amounts, and they would experience acute vitamin A poisoning within a day. Symptoms include severe headache and vomiting, blurred vision, skin sloughing off and loss of hair. There also are case reports of children becoming ill after eating large amounts of chicken liver regularly or taking cod liver oil for an extended period.

How much is too much?

Since 1941 a panel of experts from the Food and Nutrition Board of the Institute of Medicine, one of the National Academies of Sciences, has set recommended daily allowances (RDAs) for vitamins and minerals based on the minimal amounts needed to protect against deficiences. The federal government uses the panel’s recommendations to set nutrition policy, such as establishing dietary guidelines and school lunch programs. More recently, new evidence about the role of micronutrients has become available. This led the panel to come up with a new system, and starting in 1997, it began issuing a series of updated reports about the amounts of vitamins and minerals needed not only to prevent deficiencies but also to optimize health. In addition to RDAs the board established three other measures – collectively called Dietary Reference Intakes – that include adequate intake amounts, estimated average requirements and the tolerable upper intake levels.

The tolerable upper intake levels (upper limits) represent the most a healthy individual can take each day and still not be at risk of adverse health effects. It includes total intake from food, fortified food, and nutritional supplements. In establishing the upper limits, panelists looked at all available scientific evidence and used a complex risk assessment model like that applied to environmental hazards. The upper limits are still a very safe level. They’re not where you would begin to have side effects. We took the levels associated with harm and divided them by an uncertainty factor to develop a margin of safety, explains AGA member, director of the US Department of Agriculture Human Nutrition Research Center at Tufts University in Boston. Chaired IOM expert panel developed dietary reference intakes for vitamins A and K, and other micronutrients like chromium, iodine, iron and zinc.

The margin of safety for each micronutrient depends on documentation about the risk and severity of any adverse effect. For instance, the upper limit for vitamin C – 2,000 milligrams per day for adults – is 1.5 times below the threshold where adverse effects have been documented (3,000 milligrams).

The adverse effects – gastrointestinal disturbances and watery diarrhea – stop when vitamin C intake goes down. It’s self-limiting. The person stops taking it and the symptoms go away. In contrast, the upper limit for folate (1 milligram per day) is five times lower than the lowest level of observed adverse effects (5 milligrams per day) because it can mask an existing vitamin B12 deficiency or cause one to happen. When left untreated, vitamin B12 deficiency can result in permanent nerve damage. Doctor arrived at a wider safety margin because the adverse effect can be irreversible and severe. The upper limits are intended for healthy people, not for those under medical supervision who may need extra amounts of certain vitamins or minerals to address deficiencies or other medical problems.

Is it water or fat-soluble?

Aside from memorizing all the upper limits, a good rule of thumb for knowing which vitamins to be the most careful about is to distinguish between the ones that are water-soluble vitamins which include vitamin C, biotin and the sever B vitamins: thiamin (B1); riboflavin (B2); NIACIN (B3); pathothenic acid (B5), pyridoxine (B6); folate (B9 – also known as folic acid and folacin) and cobalamin (B12). These vitamins dissolve in water and any excess amounts are eliminated in urine. With the exception of pyridoxine and folate, there is no evidence at this time of any serious side-effects from water-soluble vitamins. In fact, upper limits have not been set for several of them, including biotin, B5, B2, B1 and B12. However, that shouldn’t be seen as a license to start taking mega-doses. Research is mounting that the whole package of food – nutrients acting in concert with other substances like phytochemicals and bioflavins – confers the greatest health benefits.

As a group, fat-soluble vitamins have more potential for adverse effects. Any unused amounts of vitamins A, D, E and K are not flushed out of the body like water-soluble vitamins. Instead, they’re stored in body fat and the liver, and can accumulate and eventually become toxic. Although rare, adverse effects are associated with high intake of all the fat soluble vitamins. In general, people are the most sensitive to vitamins A and D.

Aside from the short-term effects of an acute overdose, long-term risks are associated with continued high intake of vitamin A, such as birth defects and liver disease. Some research also indicates that high levels of vitamin A supplements may be associated with osteoporosis. However, these findings are controversial and for now experts have not changed recommended upper level intakes. High levels of vitamins E can act as an anticoagulant to slow the process of blood clotting. This effect can be more pronounced if the individual also takes certain medications like aspirin and warfarin or the herbal product ginkgo biloba. Too much vitamin D can lead to nausea, vomiting, poor appetite, constipation, weakness and weight loss. It also can raise blood levels of calcium, a condition known as hypercalcemia, which can cause kidney stones, kidney failure and heart rhythm abnormalities.

Major and trace minerals

The body also needs numerous minerals to function properly. Those needed in larger quantities – more than 250 milligrams each day – are considered major minerals. Examples include calcium, sodium, potassium, phosphorus, sulfur, chloride and magnesium. The RDAs for trace minerals are much lower – generally less than 20 milligrams each day. Zinc, iron, selenium, iodine, manganese, fluoride, molybdenum and copper are examples. Tiny amounts of these substances are found in a variety of foods, so it’s unlikely that you could eat your way to a toxic level. In addition, the body generally does a good job of regulating mineral levels. It has a homeostatic mechanism, so as a deficiency develops, the percentage of intestinal absorption increases. As normalcy status is achieved, the percentage of intestinal absorption decreases, explains an associate professor of medicine at Northwestern University in Chicago.

Taking supplements can overwhelm this check-and-balance system, and cause side-effects ranging from gastrointestinal disturbances in the case of too much iron, copper and magnesium to kidney diseases in the case of calcium and chromium. Excess consumption of certain minerals also interferes with the absorption of others. For example, too much zinc can result in decreased copper intake, which can affect tissue healing and thyroid function, and interfere with glucose tolerance and heart rhythms. Likewise, very high levels of calcium in the blood can decrease absorption of zinc and iron, which can lead to anemia and a weakened immune system.

Toxicity also depends on the form of the mineral. For example, sodium chromate tetrahdrate (also known as chromate of soda) is poisonous and maybe fatal if swallowed or inhaled. But organic chromium found in trace amounts in cereals, meats, poultry and fish helps maintain normal blood glucose levels.

Avoiding problems

If you are taking a vitamin or mineral supplement, in general it’s better to avoid mega-doses and instead take a simple multi-vitamin multi-mineral formula. In addition, people with pre-existing conditions like kidney or liver disease are more susceptible to adverse effects from high vitamin and mineral intake, so they should consult with their physician before starting a supplement regimen. However, your best bet for not experiencing any problems from excess vitamin or mineral intake is simply to eat a well-balanced diet with special attention to eating the recommended amounts of foods that provide vitamins and minerals such as fruits, vegetables and dairy products.