Several clinical trials suggest that acetyl-L-carnitine delays onset of ARCD and improves overall cognitive function in the elderly. In a controlled clinical trial, acetyl-L-carnitine was given to elderly people with mild cognitive impairment. After 45 days of acetyl-L-carnitine supplementation at 1,500 mg per day, significant improvements in cognitive function (especially memory) were observed.¹ Another large trial of acetyl-L-carnitine for mild cognitive impairment in the elderly found that 1,500 mg per day for 90 days significantly improved memory, mood, and responses to stress. The favorable effects persisted at least 30 days after treatment was discontinued.² Controlled^3,4,5 and uncontrolled⁶ clinical trials on acetyl-L-carnitine corroborate these findings.

In a double-blind study, supplementation with a proprietary blend of acetyl-L-carnitine, omega-3 fatty acids from fish oil, and coenzyme Q10 for 12 months resulted in an improvement in both visual function and in objective findings on eye examination (a decrease in the drusen-covered area on the retina).⁷

Several clinical trials have found that acetyl-L-carnitine supplementation delays the progression of Alzheimer’s disease,⁸ improves memory,^9,10,11 and enhances overall performance in some people with Alzheimer’s disease.^12,13 However, in one double-blind trial, people who received acetyl-L-carnitine (1 gram three times per day) deteriorated at the same rate as those given a placebo.¹⁴ Overall, however, most short-term studies have shown clinical benefits, and most long-term studies (one year) have shown a reduction in the rate of deterioration.¹⁵ A typical supplemental amount is 1 gram taken three times per day.

Several clinical trials suggest that acetyl-L-carnitine delays onset of ARCD and improves overall cognitive function in the elderly. In a controlled clinical trial, acetyl-L-carnitine was given to elderly people with mild cognitive impairment. After 45 days of acetyl-L-carnitine supplementation at 1,500 mg per day, significant improvements in cognitive function (especially memory) were observed.¹⁶ Another large trial of acetyl-L-carnitine for mild cognitive impairment in the elderly found that 1,500 mg per day for 90 days significantly improved memory, mood, and responses to stress. The favorable effects persisted at least 30 days after treatment was discontinued.¹⁷ Controlled^18,19,20 and uncontrolled²¹ clinical trials on acetyl-L-carnitine corroborate these findings.

Acetyl-L-carnitine may be effective for depression experienced by the elderly. A preliminary trial found that acetyl-L-carnitine supplementation was effective at relieving depression in a group of elderly people, particularly those showing more serious clinical symptoms.²² These results were confirmed in another similar clinical trial.²³ In that trial, participants received either 500 mg three times a day of acetyl-L-carnitine or a matching placebo. Those receiving acetyl-L-carnitine experienced significantly reduced symptoms of depression compared to those receiving placebo. At least two other clinical studies of acetyl-L-carnitine for depression in the elderly have reported similar results.^24,25 The amount typically used is 500 mg three times daily, although one trial used twice that amount.

In a double-blind study, supplementing with the combination of propionyl-L-carnitine (a form of L-carnitine) and acetyl-L-carnitine (2 grams of each per day) for six months significantly improved erectile function in elderly men with erectile dysfunction associated with low testosterone levels. Propionyl-L-carnitine and acetyl-L-carnitine were significantly more effective than testosterone treatment.²⁶

L-carnitine is a substance made in the body and also found in supplements and some foods (such as meat). It appears to be necessary for normal functioning of sperm cells. In preliminary studies, supplementing with 3–4 grams per day for four months helped to normalize sperm motility in men with low sperm quality.^27,28 While the majority of clinical trials have used L-carnitine, one preliminary trial found that acetylcarnitine (4 grams per day) may also prove useful for treatment of male infertility caused by low quantities of immobile sperm.²⁹

In a double-blind study, supplementation with a proprietary blend of acetyl-L-carnitine, omega-3 fatty acids from fish oil, and coenzyme Q10 for 12 months resulted in an improvement in both visual function and in objective findings on eye examination (a decrease in the drusen-covered area on the retina).³⁰

In a double-blind trial, supplementation with acetyl-L-carnitine in the amount of 1,500 mg per day for ten weeks was significantly more effective than a placebo in improving musculoskeletal pain, depression, and general health in people with fibromyalgia.³¹

In a double-blind study, supplementing with the combination of propionyl-L-carnitine (a form of L-carnitine) and acetyl-L-carnitine (2 grams of each per day) for six months significantly improved erectile function in elderly men with erectile dysfunction associated with low testosterone levels. Propionyl-L-carnitine and acetyl-L-carnitine were significantly more effective than testosterone treatment.³²

In a double-blind study of people with diabetic neuropathy, supplementing with acetyl-L-carnitine was significantly more effective than a placebo in improving subjective symptoms of neuropathy and objective measures of nerve function.³⁴ People who received 1,000 mg of acetyl-L-carnitine three times per day tended to fare better than those who received 500 mg three times per day.

Acetyl-L-carnitine is an amino acid that may have effects on brain chemicals and hormones that control female reproductive hormones. In a preliminary trial, 2 grams daily of acetyl-L-carnitine was given to amenorrheic women who had either low or normal blood levels of female hormones. Hormone levels improved in the women with low initial levels, and half of all the women resumed menstruating within three to six months after beginning supplementation.³⁵ Controlled trials are needed to confirm these promising results.

Acetyl-L-carnitine is an amino acid that may have effects on brain chemicals and hormones that control female reproductive hormones. In a preliminary trial, 2 grams daily of acetyl-L-carnitine was given to amenorrheic women who had either low or normal blood levels of female hormones. Hormone levels improved in the women with low initial levels, and half of all the women resumed menstruating within three to six months after beginning supplementation.³⁶ Controlled trials are needed to confirm these promising results.