(CNN)If you've been more concerned about your health lately, you might be wondering if taking a nutrition supplement containing vitamins, minerals or a combination is worthwhile.
It's estimated that more than half of Americans take one or more dietary supplements daily or on occasion.
The pills are popular in Europe, too: According to one estimate, the dietary supplement market was worth over $14 billion in 2018, although research has suggested that usage varies widely according to each country.
But are you wasting your money on vitamins and minerals you don't need or possibly harming yourself by taking high doses? Here's the lowdown.
A healthy diet comes first
Adding supplements only makes sense for some of us, experts say, such as the elderly, pregnant women, breastfeeding babies and people who have certain diseases or conditions that affect absorption of nutrients, potentially resulting in nutritional deficiencies.
In fact, mitigating nutritional deficiencies is where supplements "are best utilized" according to Craig Hopp, deputy director of the division of extramural research at the National Center for Complementary and Integrative Health, part of the US National Institutes of Health.
"Anytime somebody is missing major food groups, the first question is, can we target the missing nutrients with food? If not, then we would look into a supplement," said registered dietitian nutritionist Melissa Majumdar, who is a spokesperson for the Academy of Nutrition and Dietetics.
But there's a big difference between taking a pill as "nutritional insurance" if your diet is low in one or more nutrients versus taking it in the hopes of warding off disease. And even if you're popping a pill to simply up your vitamin C or calcium intake, health professionals agree it's not a substitute for a healthy diet.
"Eating a healthy diet is going to do far more for you than any supplement you can take, and yet we have a whole industry that is based on selling us all types of supplements," said Martha H. Stipanuk, James Jamison professor of nutrition emeritus in the division of nutritional sciences at Cornell University.
"When we look at health outcomes, no one supplement will have the effect of an overall healthy diet, in terms of immunity or chronic disease."
"Fruits and vegetables have phytochemicals and fiber; when you pop a pill, you never get the same outcomes," said Lisa Young, a registered dietitian nutritionist and adjunct professor of nutrition at New York University.
Experts worry that high doses of nutrients can give a false sense of promise.
"Often you feel you won't necessarily have to concentrate on getting these nutrients from your diet," said Young, who added that she often sees this with clients in her private practice. "You might feel like, 'This is insurance and I don't have to eat well,' and it might have a negative effect."
Supplements: The state of the science
"At the moment, evidence to support the use of individual vitamins and minerals for treatment or prevention of chronic disease outcomes is weak," Hopp said.
"A diet high in fruits in vegetables includes [lots of] vitamins and minerals ... and is epidemiologically associated with reduced instance of a whole host of chronic diseases," Hopp said. "But we have not seen that you can dietary supplement your way to good health. They are dietary supplements, not substitutes."
"There are some data that support benefits of certain supplements on specific outcomes, but many recent systematic reviews are concluding that, for most supplements, we have insufficient quality data to allow us to make strong recommendations," Stipanuk added.
Studies are usually relatively short-term — two or three years at the most — and many lack appropriate control groups, Stipanuk explained. And when there are positive outcomes in observational studies, researchers can't necessarily prove that the supplement is responsible for the beneficial effect.
"Nutrition and food are one piece of the puzzle. ... people who concentrate on eating a healthy diet tend to do other things like stress management, get adequate sleep and exercise ... so there's probably an interactive effect. And that might be why the research on supplements is so mixed," added Young, who is also the author of "Finally Full, Finally Slim."
Too much of a good thing
In fact, high doses of some vitamins and minerals — particularly vitamin A, vitamin D, niacin, folic acid, calcium and iron — can build up to toxic levels and have adverse side effects.
For example, once you are over 50, you are at very low risk of iron deficiency, and there is no need for iron supplements, Stipanuk explained, but you could develop gastrointestinal irritation or more serious iron deposition in the liver and other tissues if excess iron is routinely taken.
"We want to sway people away from taking supplements without the guidance of a registered dietitian nutritionist or medical professional that understands the pathways and interactions of a particular nutrient," said Majumdar, who added that taking too much zinc can interfere with iron or calcium absorption, and could potentially cause deficiencies of these minerals.
Too much calcium could increase the risk of kidney stones, while toxic levels of vitamin D can cause calcium to deposit in smooth muscle tissue, which is found around organs in the digestive, respiratory and reproductive tracts, Young added.
"There are upper limits of safe intake, and it's very easy to exceed those limits for some nutrients when you combine various food sources of a nutrient, including fortified foods, along with a supplement and a multivitamin," Stipanuk said.
"You don't want to be taking one thing from too many sources," Stipanuk advised. "The various sources could add up to an amount that far exceed need, and that may have an adverse effect."
And just because a supplement is promoted as "natural" doesn't necessarily mean it's safe to use, especially if you are taking medications that it can negatively interact with. For example, vitamin K will reduce the ability of blood thinners to work. If you are taking a blood thinner such as warfarin (Coumadin®), it's critical to consume about the same amount of vitamin K each day.
Additionally, research has revealed that vitamin E supplements may actually increase the risk of developing prostate cancer.
Digestive problems can occur in some people, even with proper doses. "Some say I can't take calcium carbonate because I get a stomachache or that iron is constipating," Young said.
Because each person's needs are so different, it's important to ask your doctor to refer you to a registered dietitian nutritionist. (Registered dietitian or registered dietitian nutritionist are the correct terms — technically anyone can say that he or she is a "nutritionist," but only those who have met criteria established by the Academy of Nutrition and Dietetics can call themselves an RD or RDN.)
Where supplements make sense
Here's where supplements can come in handy, according to guidelines from national health organizations. Before you add any supplements to your diet, however, meet with a health care provider who can determine what is best for you based on your individual health history and lifestyle habits.
Vegans: Vegans of any age are at risk of vitamin B12 deficiency because vitamin B12 is not produced by plants, Stipanuk explained. If you are a vegetarian, especially a vegan, you should ingest a reliable vitamin B12 source, such as fortified foods or supplements, according to the Vegetarian Nutrition Dietetic Practice Group of the Academy of Nutrition and Dietetics. The average daily recommended amount for adults is 2.4 micrograms per day.
Pregnant women: During pregnancy it's important to get an adequate amount of folic acid, which helps prevent birth defects, as well as iron, calcium, vitamin D, choline, omega-3 fatty acids, B vitamins and vitamin C, according to the American College of Obstetricians and Gynecologists.
If you are pregnant, consult your OB/GYN for a prenatal vitamin recommendation.
Postmenopausal women: If you are postmenopausal or at risk for osteoporosis and you avoid dairy and other food sources of calcium like almonds, tofu or canned salmon with bones, consider a calcium and vitamin D supplement, to help keep bones strong and reduce bone loss.
Older adults may also benefit from vitamin D supplementation because their skin doesn't make vitamin D when exposed to sunlight as efficiently as when they were young, and their kidneys are less able to convert vitamin D to its active form.
Recommendations for women 51 to 70 years of age include 1,200 milligrams of calcium and 600 international units of vitamin D; for those 71 years and older, 1,200 milligrams of calcium and 800 IU of vitamin D, according to the American Academy of Family Physicians.
According to practice guidelines from the American College of Obstetricians and Gynecologists, a vitamin D level of 20 nanograms per milliliter (50 nanomoles per liter) is recommended for good bone health.
Calcium supplements come in two forms: carbonate and citrate. Calcium carbonate is absorbed best when taken with food. Calcium citrate is absorbed well with or without food. Those with low levels of stomach acid (more common in people older than 50) absorb calcium citrate more easily than calcium carbonate.