As an antioxidant, Q10’s also improves health.  The antioxidant nature of CoQ₁₀ derives from its energy carrier function.  As an energy carrier, the CoQ₁₀ molecule is continually going through an oxidation-reduction cycle. As it accepts electrons, it becomes reduced. As it gives up electrons, it becomes oxidized. In its reduced form, the CoQ10 molecule holds electrons rather loosely, so this CoQ10 molecule will quite easily give up one or both electrons and, thus, act as an antioxidant (Wikipedia).  It is considered the best of anti-oxidants because it is distributed widely in the body and naturally serves this function.  Long-term usage is required for this benefit.   Side effects are none.

Benefits listed below are found at http://www.totalsupplement.net/category/CoQ10-88.  I have supplied the external links to journals, and made other additions.  Wikipedia and National Cancer institute are quality sources.  

After Heart Attack and Angina pain:  A clinical study found that people who took daily CoQ10 supplements within 3 days of a heart attack were less likely to have subsequent heart attacks, less chest pains, die of heart disease. The capacity for exercise  improved about 30% for those with chronic heart failure on taking Q10, also. 

Heart failure (HF):  People who have congestive heart failure, their heart isn't able to adequately pump blood, thus it pools in parts of the body, such as the lungs and legs.  “Several clinical studies suggests that Q10 supplements help reduce swelling in the legs; reduce fluid in the lungs to making breathing easier; and increase exercise capacity in people with heart failure, and reduces hospital admissions by 61%”, similar, also, long-term and safety.

High blood pressure:  In a meta-analysis of 12 clinical studies, Cochrane concluded that Q10 lowers systolic blood pressure by up to 17 mm Hg and diastolic blood pressure by 10 mm Hg, probably from improved heart functions.

Bad cholesterol:  Q10 attaches to LDL. It reduces oxidative damage and thus slows atherogenesis.  

Sperm, at Wikipedia.  A study of idiopathic infertile men found after 26 weeks of treatment compared to the placebo cohort significant increase in sperm volume, motility, improved morphology, and seminal plasma activity.  Also renal health, and gene expression controlling inflammation improved. also.

Diabetes:  Q10 supplements improves blood sugar level 31% and also lowers high blood pressure in people with type 2 diabetes.  “In conclusion, serum Q10 levels in type 2 diabetes patients are decreased and may be associated with subclinicaldiabetic cardiomyopathy reversible by CoQ10 supplementation”.

Cancer & chemotherapy:  Low levels of Q10 have been noted with several common cancers, thus it has been used as a supplement for cancer victims.  Several clinical studies found that Q10 help prevent damage caused by certain chemotherapy drugs, adriamycin, and other athracycline medications.

Heart surgery:  Clinical research indicates that introducing Q10 prior to heart surgery, including bypass surgery and heart transplantation, can reduce damage caused by free radicals, strengthen heart function, and lower the incidence of irregular heart beat (arrhythmias) during the recovery phase.

Immune system:  “Models of the immune system including phagocytic rate, antibody level, neoplasia, viral and parasitic infections were used to demonstrate that Q10 is an essential immune-modulating agent”.

Gum (Periodontal) disease:  topical CoQ10 supplements led to faster healing and tissue repair.

Parkinson's disease & Neuronal health:  slows the progress:  “Those who took 1,200 mgs daily had 44% less decline in mental function, motor function.”   Q10 also lowers the risk of various other neurodegenerative diseases by reducing neurotoxic insult.  Long-term usage should lower the risk Alzheimer’s and vascular dementia. 

Migraines:  Help prevent migraines  Thirty-one patients completed the study; 61.3% of patients had a greater than 50% reduction in number of days with migraine headache. The average number of days with migraine during the baseline period was 7.34 and this decreased to 2.95 after 3 months of therapy. Mean reduction in migraine frequency after 1 month of treatment was 13.1% and this increased to 55.3% by the end of 3 months.    

Macular Degeneration (the leading cause of blindness in seniors):  “Mitochondrial dysfunctions have been implicated in the pathophysiology of several age-related diseases including age-related macular degeneration(AMD), a progressive neurodegenerative disease affecting primarily the retinal pigment epithelium (RPE).  AMD may also develop in normal aging, 10–15 years after appearing in AMD patients.  CoQ10 levels in the retina can decline by approximately 40% with age.”  Moreover Vitamin A & E, or mineral supplements selenium and zinc wereNOT shown to delay AMD.

Statin induced Myopathy (muscle weakness and pain) and other side effects:  Statins inhibit the mevalonatepathway, which effects both the production of cholesterol and of Q10 by over 40%.  Thus statins reduce ATP, the body’s source for energy including those that drive bodily synthesis.  In the elderly (over 60) this effect is pronounced.   Reduction in Q10 (thus ATP) accounts for the long list and high frequency of side effects.  Statins are incompatible with the maximal exertion of elite athletes.   Myopathy is ameliorated by Q10 supplementation.  Statins is poorly tolerated by the elderly.

Physical endurance:  “Results indicate that acute and chronic supplementation of Q10 may affect acute and/or chronic responses to various types of exercise”; confirmed in a study of elite athletes, as “incompatible”.

Longevity:  in rats an increased maximum lifespan of 24%, and results obtained with CoQ9.

What should be done?  The evidence clearly supports the use of Q10.  Based on clinical studies 100 mgs is sufficient; but given the lack of side effects more should be taken.  Economical sources are Puritan Pride and Costco, their sale prices are comparable   Peak blood level is in 2-6 hours, and second peak at about 24 hours; half-life is 33 hours.  Does not interact with other drugs or have side effects, and has been shown safe at 2,400 mgs.  “The use of the aqueous suspension of CoQ₁₀ has only a minor effect” Q10 is dissolved in oil.    Since absorption testing is usuallly done by the manufacturer, claims are suspect.  Aqueous versions are marketed.   The synthesis of an intermediary precursor of coenzyme Q₁₀, mevalonate, is inhibited by some beta blockers (blood pressure-lowering medication)^[23] statins, and other drugs.  Large dose of vitamin e partial inhibits the anti-oxidative effect of Q10.  There is extensive positive short-term research on Q10, but no long-term population studies.  However, given its role as a ubiquitous antioxidant, benefits are likely, especially in the mitochondria.   For this reason it should be taken long-term starting by the age of 20 so as slow the rate of oxidative damage to the mitochondria, even though the decline in ATP due to damage won’t be noticed until the 5^th or 5^th decades, when endurance dramatically declines.   At the same time Q10 also prevents oxidative damage of LD, thus preventing atherosclerosis.  Q10 also protects other tissues, such as nerves from oxidative damage.  Its usage is far greater in Japan and Europe.  JK take 200-300 mg daily and wish he had started decades earlier.