In one sentence, describe what the following article is about:

When the body does not absorb or make  sufficient carnitine, doctors will prescribe oral L-carnitine. Carnitine levels may be low because of many reasons. Genetic disorders are the most common, but medical procedures such as hemodialysis also drain the body of L-carnitine temporarily. Vegetarians or anyone who is on a strict diet may also have low carnitine levels. Patients with serious kidney disease often have low red blood cell counts. Taking L-carnitine supplements is proven to be an effective way to increase red blood cell counts in these patients. Kidneys are responsible for synthesizing carnitine in the body. Kidney disease decreases carnitine and lowers red blood cell count. If you struggle with complications related to heart disease and heart failure, your doctor may prescribe L-carnitine, especially if you have chest pain or have had a heart attack. There is strong evidence that suggests L-carnitine supplements mitigate symptoms.  Patients with stable angina may benefit from L-carnitine supplements when it is taken with propionyl-L-carnitine. Both may reduce symptoms and improve the ability to exercise without chest pain. Heart attack victims benefit from L-carnitine  supplements when taken with conventional medications. It may reduce the risk of a second heart attack, chest pain, abnormal heart rhythms or heart failure. Patients who have experienced heart failure may benefit from L-carnitine. This supplement may improve exercise capacity. Studies suggest that a low dose of L-carnitine can help infants born prematurely and with a low birth weight by... The supplement can help infants get more benefit from the nutrition supplied to them at the hospital. Patients on anti-seizure medications containing valproic acid may be able to minimize and prevent side effects from that medication.  However, L-carnitine has been linked to an increased risk of seizures in patients prone to seizures, so using the supplement to combat side effects associated with anti-seizure medication can be dangerous and should only be done under doctor's supervision. L-carnitine may mitigate side effects associated with AZT (an HIV/AIDS medication), doxorubicin (chemotherapy medication), and isotretinoin  (acne medication). Research is needed to verify these claims before L-carnitine can be recommended in these cases. If you suffer hyperthyroidism, your thyroid gland produces excess hormone and you may have symptoms of nervousness, weakness, tremors and rapid heartbeat. Research indicates that L-carnitine reduces these symptoms. Research also suggests that carnitine might block the action of thyroid hormone, which is why the effect of excess thyroid hormone is reduced when it is taken. L-carnitine supplements may help correct male infertility problems caused by inflammation of the prostrate, seminal vesicles and epididymis.  Low sperm count has been linked to low levels of carnitine. L-carnitine supplements may increase sperm count and mobility.  Propionyl-L-carnitine may help men suffering erectile dysfunction, especially if they are also using conventional medication for this condition. L-carnitine has been used to treat many conditions in the past, but medical studies have either ruled the supplement to be ineffective or results were inconclusive for those conditions.  Studies suggest that L-carnitine does not improve athletic ability. There is no evidence that L-carnitine improves athletic performance or endurance. L-carnitine is often marketed as a weight loss supplement, but there is no evidence to back weight loss claims.  While the verdict may change favorably in the future, there is insufficient evidence to support claims that L-carnitine can improve:  Fatigue due to celiac disease, age, cancer, hepatitis C, or memory disorders. Leg pain caused by poor circulation (peripheral vascular disease). Some studies suggest propionyl-L-carnitine may reduce symptoms of PVD, but evidence is still inconclusive. Symptoms of attention deficit-hyperactivity disorder. Rett syndrome. Eating disorders. Diabetes. Preliminary studies indicate that acetyl-L-carnitine may reduce pain associated with diabetic neuropathy, but evidence remains inconclusive. High cholesterol. Blood disorders. Leg ulcers. Lyme disease. Autism.

Summary:
Boost low carnitine levels. Increase red blood cell count. Combat heart disease. Improve birth weight. Prevent side effects. Treat symptoms of high thyroid hormone. Treat male infertility. L-carnitine will not improve some conditions.