Maybe you feel a cold coming on or you're a little sluggish. Everyone knows about the common cold-busting powers of vitamin C and zinc, right? And of course, you've heard that CoQ10 or vitamin D can boost energy. But before you head down to your local pharmacy, it's time to dig a little deeper about when — and if — you should take these or any other supplements.

First, let's do a little myth-busting. Multiple studies have found that taking vitamin C doesn't have any consistent benefit in preventing — and may only minimally reduce the duration and severity of — the common cold. According to the National Center for Complementary and Integrative Health, if you take zinc lozenges within 24 hours of the first signs of a cold, it may help reduce the cold's duration, but excess zinc can cause serious side effects.

Supplements like CoQ10 (also known as coenzyme Q10) and vitamin D only help boost energy in people who have a deficiency in these substances. Unless your doctor has told you that you are deficient in either of these, you may want to make an appointment with your primary care physician if you aren't able to solve the mystery of your fatigue.

What are supplements?

The Food and Drug Administration (FDA) defines dietary supplements as products taken by mouth that include dietary ingredients, such as vitamins, minerals, herbs, amino acids and enzymes. These are often sold as pills, liquids, powders, gummies, etc.

In the U.S., 3 in 4 adults and 4 in 5 older adults regularly take supplements. One in 3 children takes supplements, according to the FDA. No wonder dietary and herbal supplements are a booming multibillion-dollar industry. But surprisingly, it is not as regulated and standardized as you might think.

The FDA is still working to reign in supplements, which are less regulated than medications. Because they are not intended to treat diseases or health conditions, they are not required to go through rounds of clinical and safety trials. However, supplement labels can't legally claim to treat certain conditions, but instead can only cite research on the key ingredient. Claims on supplement labels are intentionally vague, including statements such as "supports circulatory health" or "healthy immune support."

Buyer beware! You must read the small print. Products may differ significantly from what was tested in research studies. Also, you may not be getting what you think you are. Or the amount of the supplement found to provide benefit may be significantly higher than the serving size found on the label.

To help cut through the hype, registered dietitian nutritionist Amanda Beaver at Houston Methodist Wellness Services answers some questions about supplements.

Who should and should not take vitamins and other supplements?

Some people may need to take vitamins:

• Those who can't get enough vitamins from food or don't like certain food groups. Examples include older adults who may struggle to meet vitamin needs from food, individuals with GI conditions who have trouble absorbing nutrients, and children or adults who avoid many food groups because of food preferences.
• Vegetarians and vegans. Plant-foods do not contain vitamin B12, so this vitamin needs to be supplemented. Those who avoid meat should also seek out foods containing zinc, calcium, vitamin D, iron, omega-3 fats and iodine, or consider taking a supplement.
• Pregnant and breastfeeding women, and women who are trying to become pregnant. Folic acid is critical for preventing neural tube defects, iodine is needed for a fetus's brain development, and iron is needed to provide adequate blood oxygen supply to the fetus.
• People with vitamin deficiencies. People with vitamin deficiencies should take the vitamins directed by their doctor. In my practice, I have seen many patients with deficiencies in vitamin D, iron and vitamin B12.
• People who don't go outside often. Our skin makes vitamin D from sun exposure — especially during the summer months. Having darkly pigmented skin, wearing lots of sunscreen and covering up, staying mainly indoors, or living far from the equator may predispose individuals to vitamin D deficiency.
  
  

To get a better idea if you are not getting enough vitamins from food, meet with a registered dietitian who can give you very specific guidance on what your diet is lacking. Consult with your doctor and registered dietitian before taking a new vitamin, as some vitamins can interact with medications, such as thyroid medicine with calcium and iron supplements.

Can taking supplements be dangerous for some people?

There are several situations or medical conditions where individuals should avoid certain vitamins:

• Kidney disease. Ask your doctor if you should take a kidney-specific vitamin, as some supplements may contain too much potassium, vitamin C and/or phosphorous for individuals with kidney disease.
• People who smoke. These individuals should avoid high doses of beta-carotene, which has been linked to an increased risk of lung cancer in smokers.
• Hemochromatosis. People living with this condition should avoid supplements with iron and vitamin C. Instead, they should get recommended amounts of vitamin C from food.
• People who take medications. Talk to your doctor, pharmacist and a registered dietitian to see what vitamins interact with your medications. Some vitamins may need to be taken a few hours apart from the medication to allow for proper absorption of each.
  
  

Make sure to ask your doctor if you should avoid certain supplements due to a medical condition or medications.

What are the health risks associated with taking vitamins we don't need?

People hear about how they can improve their health by boosting certain vitamins or minerals, and may go out and start taking them without blood work confirming low levels or consulting a doctor. But there can be health risks associated with taking vitamins you don't need.

The risk of taking excess levels of vitamins depends on the vitamin and any health conditions you have.

Water-soluble vitamins, including B vitamins and vitamin C, can be removed from the body in our urine, so they are less likely to cause problems. However, taking high doses can still cause side effects. For example, excessive vitamin C can cause nausea, diarrhea and abdominal cramps.

Meanwhile, fat-soluble vitamins can be stored in our body's tissues. For this reason, taking excessive doses of vitamin A, D and E can be detrimental to our health, as our body has a harder time getting rid of them.

For most healthy people, the great thing about getting vitamins from a varied diet is that you don't have to worry about excess vitamins. Most foods in typical portion sizes tend to have levels of vitamins the body can handle. Not to mention, foods also tend to come packaged with a bunch of beneficial nutrients at once. For example, spinach is rich in vitamins K, A and E, as well as folate and magnesium.

Does it matter what supplement brand I choose?

Remember, not all supplements are created equal. The supplement industry is not regulated to the same standards as the pharmaceutical industry. Some supplements can contain contaminants or may not have the level of vitamins as advertised. For this reason, I recommend my patients choose a supplement that has been third-party tested for purity and quality. Examples of these third-party labs include USP-verified supplements and Consumer Lab-tested supplements.