Nearly half of women take herbal or dietary supplements daily, and these over-the-counter products are a booming industry. Herbal dietary supplement sales reached $6 billion yearly

Certain supplements may improve your health, but others can be ineffective or even harmful.

“Buyer beware,” warns JoAnn Manson, MD, chief of the division of preventive medicine at Brigham and Women’s Hospital in Boston, and professor of medicine at Harvard Medical School. “Many supplements on the market have not been rigorously tested. Very few supplements have shown to be of benefit,” says Dr. Manson. She adds that many carry unsubstantiated health claims.


Here are seven supplements you should take carefully, if at all:

1. Vitamin D: Too Much Can Harm Your Kidneys

Vitamin D promotes calcium absorption in the body, and getting enough is central to health and wellbeing. Supplemental vitamin D is popular, offering the promise of  protecting bones and preventing bone diseases like osteoporosis. But in many cases, healthy post-menopausal women who take low-dose vitamin D supplements (up to 400 international units, IU) might not actually need them.

As Manson notes, enthusiasm for high-dose vitamin D supplements is outpacing evidence. “More is not necessarily better when it comes to micro-nutrient supplements,” says Manson.

After looking at the evidence, it turns out that when healthy women take low doses of vitamin D, it does not necessarily prevent them from breaking bones. These results come from the U.S. Preventive Services Task Force report published in the Annals of Internal Medicine.

The outlook is different for women who are over the age of 65, are deficient in vitamin D, or have a history of falls or osteoporosis. For them, the Institute of Medicine says, vitamin D supplements prescribed by a doctor are beneficial.

One risk of getting too much vitamin D is that in healthy people, vitamin D blood levels higher than 100 nanograms per milliliter (ng/mL) can trigger extra calcium absorption — and lead to kidney stones, notes the Cleveland Clinic. And a February 2013 report by the U.S. Preventive Services Task Force found that postmenopausal women who took daily vitamin D and calcium supplements had a 17 percent increased risk of kidney stones compared to women who took a placebo.

To achieve vitamin D recommendations established by the Institute of Medicine – 600 IU per day for people 1 to 70 years old and 800 IU per day for individuals 71 or older – include whole foods such as salmon, tuna, milk, mushrooms, and fortified cereals in your daily diet.

2. St. John’s Wort: Avoid Drug Interactions

St. John’s wort is a plant used as a tea or in capsules to treat mild depression, anxiety, and sleep disorders. Although small studies have shown St. John’s wort to be effective at treating mild depression, a large 2011 study co-sponsored by the National Institute of Mental Health concluded that the herbal remedy did no better than a placebo at decreasing symptoms of minor depression.

Researchers suggest that improvements in depression symptoms as a result of taking St. John’s wort may have to do with the placebo effect. The NIH reports that patients’ beliefs about whether they were taking a placebo or St. John’s wort influenced their depression more so than what they actually received.

But, Denise Millstine, MD, director of integrative medicine at Mayo Clinic in Scottsdale, Arizona says, “The biggest issue with St. John’s wort is its medication interactions.”


A July 2014 study in the Journal of Alternative and Complementary Medicine found that 28 percent of the time St. John’s wort was prescribed between 1993 and 2010, it was administered in dangerous combinations with antidepressant or antianxiety medications, statins, or oral contraceptives.

Taking St. John’s wort can also reduce the effectiveness of your other medications — including birth control pills. It is important to read through literature on drug interactions and talk to your doctor before taking St. John’s wort.

3. Calcium: The Excess Settles in Your Arteries

Calcium is central for strong bones and a healthy heart, but too much is not a good thing. “Get calcium from your diet if you can,” says Dr. Millstine. Research shows that calcium is better absorbed through food. The National Institutes of Health (NIH) recommends 1,000 milligrams (mg) of calcium a day for women aged 19 to 50 and 1,200 mg a day for women 51 and older. Yogurt contains about 207 mg of calcium in 4 ounces, one-fifth of the daily recommendations. Other good calcium sources include milk, cheese, and fortified cereal and juices.

Calcium deficiency or hypocalcemia may be detected by routine blood tests. If you have low calcium blood levels, your doctor may prescribe a calcium supplement.

However, an excess of calcium, which is described by the NIH as more than 2,500 mg per day for adults ages 19 to 50, and more than 2,000 mg per day for individuals 51 and over, can lead to problems. According to the Cleveland Clinic, “Researchers believe that without adequate vitamin D to help absorb it, the extra calcium settles in the arteries instead of the bones.”

4. Multivitamins: No Substitute for a Healthy Diet

Many people believe that they do not get enough vitamins and minerals from their diet. However, the jury’s still out on whether these supplements are beneficial.

An October 2011 study published in the Archives of Internal Medicine examined data from nearly 40,000 women over 19 years. Surprisingly, researchers found that, on average, women who took supplements had an increased risk of dying compared with women who didn’t take supplements. Multivitamins did little or nothing to protect against common cancers, cardiovascular disease, or death.


However, more recent research has found benefits to taking multivitamins. In a January 2015 study in the Journal of Nutrition of more than 8,000 men and women over the age of 40, women who took a multivitamin for three or more years had a lower risk of heart disease.

For women of childbearing age, taking prenatal vitamins with folic acid is recommended to help prevent birth defects. Multivitamins might also be prescribed by your doctor if you have malabsorption syndrome, a condition in which the body does not properly absorb vitamins and minerals.

But for healthy people, Manson notes, “A supplement can never be a substitute for a healthy diet.”

5. Fish Oil Supplements: Choose Fish or Flaxseed Instead

Rich in omega-3 fatty acids, fish oil has been touted as a means to reduce heart disease. However, more and more evidence shows that fish oil supplements have questionable heart benefits. A May 2013 study in the New England Journal of Medicine gave 6,000 people at high risk for cardiovascular disease 1,000 mg of omega-3 supplements per day for five years. In the end, however, the high-risk group fared no better in terms of cardiovascular death rates than participants who received a placebo.

Taking a supplement is no substitute for a healthy diet.

Doctors agree that the best way to get your omega-3s is from food. According to the Mayo Clinic, eating fish, which is rich in omega-3 fatty acids, seems to provide more benefit to your heart health than taking supplements. And the American Heart Association (AHA) Dietary Guidelines recommend including two servings of fish per week in your diet.

For people with heart disease, the AHA recommends having 1 gram (gm) of omega-3s per day. If you have high triglycerides, the AHA recommends 2 gm to 4 gm in the form of doctor-prescribed supplements. Other sources of omega-3s beside fatty fish include flaxseeds, walnuts, and avocados.

6. Kava-Kava: Side Effects Can Harm Your Liver

Kava-kava is an herb that comes from roots of the plant Piper methysticum, and in concentrated forms, the herb has been used to treat anxiety and insomniawith mixed results. A 2014 review of alternative medicines for the treatment insomnia in Osteopathic Family Physician found that herbs including kava-kava could play an important role in the treatment of insomnia. It included results from the 1990s and early 2000s that have shown that the herb can reduce anxiety and improve sleep quality in patients with insomnia and restlessness.

However, kava-kava can have serious side effects. According to the United States National Library of Medicine, “Products labeled as kava have been linked to the development of clinically apparent acute liver injury which can be severe and even fatal.”

In March 2002 the U.S. Food and Drug Administration issued a warning about the effects of kava-kava on the liver, prompting the National Center for Complementary and Integrative Health to suspend all studies on the supplement. Kava-kava has also been associated with abnormal muscle spasms, and interacts with a number of additional drugs, including anticonvulsants, antipsychotic medications, and drugs used for Parkinson’s disease.

7. Soy Isolate: Careful With the Estrogen

Tofu, tempeh, and soy milk are all great sources of protein, fiber, and a number of minerals. Some women also take soy in supplement form to relieve symptoms of menopause. However, concerns have been raised about soy supplements because studies have shown that they may contribute to an increased risk of breast cancer due to the estrogen they contain. The American Cancer Society notes, “Research on soy and cancer is highly complex, controversial, and evolving.”

“If you’re concerned about breast cancer, stay away from soy supplements and soy-based protein,” Millstine says. “Soy intake from foods has not been shown to be of concern though.”