L-Carnitine, Acetyl-L-Carnitine and Cognitive Function in Humans

Afraid of age-related mental decline? Carnitine supplements may help. (Photo by qmnonic)

In the previous post, we looked at the animal studies on carnitine and its effect on cognition. The results were generally positive: both L-carnitine and acetyl-L-carnitine protect the brains of rodents from the effects of aging and stress.

Since, however, we're more interested in whether carnitine is useful as an anti-aging brain supplement in humans, it's time to look at human studies. All the relevant papers related to humans and cognition I could find from the past three decades are briefly discussed below.

Carnitine and age-related cognitive decline

Cipolli & Chiari studied the effects of acetyl-L-carnitine on mildly impaired elderly people. The subjects were given 1.5 g of ALCAR for two periods of 45 days. They report that ALCAR was effective in improving memory function and constructional thinking, while its effect on relational behavior was less consistent.

Long-term oral treatment with acetyl-L-carnitine seems to slow the progression of Alzheimer's disease as well. Spagnoli et al. report that while both the control group and the ALCAR-treated group had worsened after one year, the subjects receiving ALCAR showed a slower rate of cognitive deterioration in all measures, including verbal critical abilities and long-term verbal memory.

Thal et al. note that patients with Alzheimer's disease treated with 3 g of ALCAR per day declined at the same rate as the control group on all measures. A closer look revealed that early-onset patients on ALCAR declined more slowly than those on placebo, while late-onset patients responded poorly. The authors suggest that acetyl-L-carnitine may help AD patients aged 65 or younger but not older patients.

Later, however, Thal et al. treated early-onset AD patients (45 to 65 years old) with 1 g of ALCAR daily for one year and found little to no improvement in cognitive ability compared to the control group. Only the Mini Mental State Estimation (MMSE) showed a decrease in deterioration.

On the other hand, Passeri et al. report that mildly demented patients aged over 65 years showed significant improvement in behavioural scales, memory tests, attention barrage test and verbal fluency test. The treated group received 2 g of ALCAR daily for two months. Thus, perhaps the severity of the dementia is also a factor when determining the effectiveness of ALCAR.

In a really long-term study by Rai et al., patients with Alzheimer's disease were given either 2 g of ALCAR or placebo for two years. The differences between groups were small; the authors suspect this was due to the small sample size (only 20 patients). Still, there was a trend for less deterioration in the treated group, especially in short-term memory tasks.

L-carnitine may even work in those who have had their 100th birthday. Malaguarnera et al. report that 2 grams of L-carnitine resulted in significant improvements in mental fatique and MMSE compared to the control group. They also reduced their fat mass, increased their muscle mass, and had less physical fatique.

Carnitine and depression

In an old study, Bella et al. gave sixty senile subjects (aged 60-80 years) suffering from depressive symptoms either 3 g of acetyl-L-carnitine or placebo daily. After two months of treatment, the severity of depressive symptoms and quality of life as measured by a questionnaire had improved significantly compared to the control group.

Similar results are reported by Tempesta et al. who treated patients suffering from depressive syndrome with ALCAR for a month. ALCAR treatment was highly effective in reducing depressive tendencies. General somatic symptoms and anxiety, asthenia and sleep disturbances were largely unaffected, however. Unfortunately, the dose used by the authors is not mentioned in the abstract, and the full paper is so old that I'm unable to access it.

Carnitine and other neuropsychological problems

Cirrhosis patients often have disturbances in mental state and neuromuscular function. Malaguernerna et al. studied the effects of ALCAR on cirrhosis patients by giving them either acetyl-L-carnitine or placebo. After 90 days, the ALCAR group showed improvements in neuropsychological functioning and greater reductions in serum ammonia levels.

Persons with Down syndrome are at a greater risk to develop Alzheimer's disease. Pueschel studied the effects of acetyl-L-carnitine on neurological, intellectual and social functions in adults with Down syndrome. In this case, ALCAR administration did not improve central nervous system functions.

Carnitine in young, healthy people

All of the studies so far have been dealing with old or otherwise impaired people. The results suggest carnitine has a protective role in brain functioning, but what about healthy people? Unfortunately, the data is very lacking. In fact, I could find only one study that looked at the cognition-boosting effects of carnitine in young, healthy participants.

In an unpublished research paper, Rohde describes an experiment where college students were given either 1 g of ALCAR in two 500 mg doses or placebo daily for two weeks. Their cognitive ability was then tested on a computer software. The ALCAR group out-performed the controls on 83% of the measures, which suggests acetyl-L-carnitine may indeed be helpful for those still have all their mental capacity.

However, since this is an unpublished study, and there are no other studies available, I would be fairly cautious about the results. Also, there's at least one study that showed carnitine had no effect in young rats. Nonetheless, some people without cognitive problems report increased physical and mental energy from taking ALCAR, so perhaps there's something to it. A human experiment may be in order to find out for myself.

Conclusion

Most of the studies on acetyl-L-carnitine show a benefit in treating mental decline and Alzheimer's disease, although a few studies reported no effects. It is unclear whether ALCAR works better in younger AD patients. L-carnitine was shown to reduce mental and physical fatique even in those aged over 100 years, however.

ALCAR also seems to relieve symptoms and improve quality of life in patients suffering from depression. The data for neuropsychological problems resulting from other diseases is mixed. One unpublished paper suggests ALCAR in two 500 mg doses may improve cognition in healthy, young people.

Taken together with the animal studies, the results suggest acetyl-L-carnitine and L-carnitine can reverse some of the effects of aging and possibly causes as well.

For more information on brains and aging, see these posts:

L-Carnitine, Acetyl-L-Carnitine and Cognitive Function in Animals
Increasing Intelligence by Playing a Memory Game – Experiment Update
Caloric Restriction Improves Memory in the Elderly
Moderate and Severe Caloric Restriction Alter Behavior Differently in Rats