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NCCIH Clinical Digest

for health professionals

Myth-Busting Popular Natural Products Marketed for Disease Prevention and Wellness: What the Science Says

January 2017

Clinical Guidelines, Scientific Literature, Info for Patients: 
Myth-Busting Popular Natural Products Marketed for Disease Prevention and Wellness

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Improving Sleep Problems

Myth: Herbs such as valerian, chamomile, and kava are effective for insomnia.

Fact: Various herbs such as valerian, chamomile, and kava, and homeopathic medicines sometimes used as sleep aids have not been shown to be effective for insomnia, and important safety concerns have been raised about a few. For example, kava supplements have been linked to a risk of severe liver disease.

However, there is evidence to suggest that using relaxation techniques, such as progressive relaxation, guided imagery, biofeedback, or deep breathing exercises, before bedtime can be helpful components of a successful strategy to improve sleep habits. Current evidence also suggests that melatonin may be useful in treating several sleep disorders, including jet lag, delayed sleep phase disorder, and sleep problems related to shift work.

Reducing Stress

Myth: The herb passionflower can reduce stress and improve overall health.

Fact: There are very few clinical trials of passionflower and therefore insufficient evidence to determine whether passionflower is efficacious for any condition.

However, there is some scientific evidence to date that suggests mindfulness meditation—a mind and body practice which cultivates abilities to maintain focused and clear attention, and develop increased awareness of the present—may help reduce symptoms of stress, including anxiety and depression. Results from a small body of research suggest that yoga may also affect stress and anxiety symptoms.

Preventing Colds

Myth: A daily dose of a vitamin C supplement will prevent the onset of the common cold.

Fact: Several reviews have concluded that prophylactic vitamin C does not reduce the incidence of colds in the general population, but may be useful in reducing incidence of colds for people exposed to brief periods of severe physical exercise (e.g., marathon runners, skiers, and soldiers training in subarctic conditions).

Reducing Cholesterol Levels or Other Known Cardiovascular Disease Risk Factors

Myth: Taking garlic supplements will prevent heart disease.

Fact: There is no evidence that garlic supplements prevent heart disease. Evidence is mixed about whether garlic supplements lower cholesterol levels or or change other known cardiovascular disease risk factors.

Preventing Cognitive Decline

Myth: Turmeric (curcumin) and Ginkgo biloba supplements can prevent the onset of dementia and Alzheimer’s disease in people.

Fact: Although there is some evidence in laboratory studies that curcumin may affect brain function and the development of dementia, these results have not been demonstrated in clinical trials. In several large clinical trials, Ginkgo biloba has been shown to be ineffective in reducing either the overall incidence rate of dementia or Alzheimer’s disease incidence.

NCCIH Clinical Digest is a service of the National Center for Complementary and Integrative Health, NIH, DHHS. NCCIH Clinical Digest, a monthly e-newsletter, offers evidence-based information on complementary health approaches, including scientific literature searches, summaries of NCCIH-funded research, fact sheets for patients, and more.

The National Center for Complementary and Integrative Health is dedicated to exploring complementary health products and practices in the context of rigorous science, training complementary health researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCIH’s Clearinghouse toll-free at 1-888-644-6226, or visit the NCCIH website at NCCIH is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.


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