Coenzyme Q10 is unlike most other dietary supplements in that it actually occurs naturally in humans and most mammals. Coenzymes are molecules that are needed for the functioning of enzymes; enzymes are molecules that speed up chemical reactions in the body. Coenzyme Q10 exists in the mitochondria of cells and is involved in chemical reactions that generate energy for cell growth and maintenance. It also functions as an antioxidant. Antioxidants neutralize so-called free radicals, which are highly reactive chemicals that can damage the DNA in genes and have been linked to cancer.
Coenzyme Q10 is synthesized in the body and is found in all animal tissues; there is no need for healthy people eating a varied diet to supplement their food intake to obtain it. Low levels of Coenzyme Q10 have been detected in patients with cancer and heart failure and this has served as a rationale in and of itself for treating patients with these diseases with Coenzyme Q10. This is not logical. Cancer patients typically have low red blood cell counts and low levels of albumin in their blood; it does not follow that blood transfusions or administering albumin will cure them. As always, the best way to assess whether a chemical effectively treats a disease is to subject it to a randomized, controlled trial. The FDA has warned one Coenzyme Q10 manufacturer not to claim that the supplement is effective for heart disease.
On March 4, 2005, the Food and Drug Administration (FDA) denied two citizen’s petitions that would have required the professional product labeling for the cholesterol-lowering “statin” drugs to recommend that the dietary supplement coenzyme Q10 be added to statin therapy to reduce the risk of muscle damage, heart damage and congestive heart failure. They found that there was not significant evidence to suggest that coenzyme Q10 levels are responsible for the adverse effects associated with statin use or that supplementation with coenzyme Q10 has any impact on preventing or lessening any of the potential adverse effects of the statin drugs.
Claims for the use of Coenzyme Q10 in cancer rest on the observation that cancer patients have low levels of the coenzyme (see above) and some clinical observations. These are either small numbers of case reports or unblinded, uncontrolled studies in which selected patients taking other regimens for cancer had supposed decreases in tumor size or even cure. As the National Cancer Institute notes, “No report of a randomized clinical trial of coenzyme Q10 as a treatment for cancer has been published in a peer-reviewed, scientific journal.”
Reduce Toxicity of Cancer Chemotherapy
The only obtainable study examining whether the administration of Coenzyme Q10 could reduce the heart toxicity of the chemotherapeutic agent doxorubicin (ADRIAMYCIN) is a nonrandomized study with a very high loss to follow-up, which often biases the results.
Congestive Heart Failure
A number of early studies claimed that Coenzyme Q10 could benefit patients with congestive heart failure,, or improve heart output after heart surgery. However, these studies followed small numbers of patients or used measures of heart output that were vague or are no longer considered acceptable, and other early studies showed no impact of Coenzyme Q10.
Two more recent, better designed studies have undermined the credibility of these effectiveness claims. In one three-month study, patients with congestive heart failure randomized to Coenzyme Q10 had similar changes in measures of their heart function (e.g., ejection fraction, cardiac volume, quality of life) as patients randomized to placebo, although the study was small. In a larger, six-month study, Coenzyme Q10 similarly had no effect on measures of heart function (e.g., ejection fraction, peak oxygen consumption, exercise duration). The claimed effectiveness of Coenzyme Q10 thus remains unproven.
High Blood Pressure
Two studies claim significant blood-pressure-lowering effects for Coenzyme Q10, one in a study of hypertensive patients and another in those in which only the higher number is elevated (isolated systolic hypertension). These studies are relatively short-term and fall well short of what the FDA would require to approve an antihypertension drug. For example, they do not explore a range of Coenzyme Q10 doses.
A single randomized study published in 1998 claims to have shown that, among patients admitted to hospital with suspicion of a heart attack, Coenzyme Q10 can reduce subsequent fatal and nonfatal heart attacks. However, follow-up was short, the placebo and treatment capsules were not identical, and the authors claim an unlikely 100% follow-up rate (or they are only reporting on patients they did recontact, which is not methodologically acceptable). The authors conclude that “More studies in a larger number of patients and long-term follow-up are needed to confirm our results.” We were unable to locate any such study.
Two randomized studies claim benefits upon blood sugar control in diabetes. However, the first did not measure hemoglobin A1C (HbA1C), which measures average glucose control over an approximately three-month period, and the second showed only a small improvement in HbA1C but no impact upon fasting blood sugar or insulin levels. Two small studies with longer follow-up showed no impact of Coenzyme Q10 on HbA1C.,
A randomized, controlled trial reported a trend toward a small benefit on a scale that measured Parkinson’s disease symptoms, but no impact upon the rate at which these patients with early disease began to need treatment with levodopa.
In 2014, a randomized controlled clinical trial published in JAMA Neurology on the use of high-dose Coenzyme Q10 in patients with early Parkinson’s disease found that the drug did not show any evidence of clinical benefit in these patients.
The only randomized controlled trial showed no impact of Coenzyme Q10 on the rate of functional decline in Huntington’s disease.
Interactions with Other Drugs
The 2003 edition of Evaluations of Drug Interactions and a published medical journal article list warfarin (COUMADIN, JANTOVEN) as interacting with Coenzyme Q10.
Coenzyme Q10 is generally well tolerated. Infrequent adverse effects have included inability to sleep, liver enzyme elevations, rashes, nausea, and abdominal pain.
Despite the plethora of claimed uses, not a single potential indication has adequate evidence to support the clinical use of Coenzyme Q10.