Carnitine supplements do not improve oxygen consumption or metabolic functions when exercising, nor do they increase the amount of carnitine in muscle. There is no evidence that L-carnitine influences fat metabolism or aids in weight loss. Male fertility
The carnitine content of seminal fluid is directly related to sperm count and motility, suggesting that the compound might be of value in treating male infertility. Diseases
Carnitine has been studied in various cardiometabolic conditions, indicating it is under preliminary research for its potential as an adjunct in heart disease and diabetes, among numerous other disorders. Carnitine has no effect on preventing all-cause mortality associated with cardiovascular diseases, and has no significant effect on blood lipids.Although there is some evidence from meta-analyses that L-carnitine supplementation improved cardiac function in people with heart failure, there is insufficient research to determine its overall efficacy in lowering the risk or treating cardiovascular diseases.There is only preliminary clinical research to indicate the use of L-carnitine supplementation for improving symptoms of type 2 diabetes, such as improving glucose tolerance or lowering fasting levels of blood glucose.The kidneys contribute to overall homeostasis in the body, including carnitine levels. In the case of renal impairment, urinary elimination of carnitine increasing, endogenous synthesis decreasing, and poor nutrition as a result of disease-induced anorexia can result in carnitine deficiency. Carnitine has no effect on most parameters in end-stage kidney disease, although it may lower C-reactive protein, a biomarker for systemic inflammation.
Metabolic defects of fatty acid oxidation
More than 20 human genetic defects in fatty acid transport or oxidation have been identified. In case of fatty acid oxidation defects, acyl-carnitines accumulate in mitochondria and are transferred into the cytosol, and then into the blood. Plasma levels of acylcarnitine in newborn infants can be detected in a small blood sample by tandem mass spectrometry.When β oxidation is defective because of either mutation or deficiency in carnitine, the ω (omega) oxidation of fatty acids becomes more important in mammals. Actually, the ω Oxidation of Fatty Acids is another pathway for F-A degradation in some species of vertebrates and mammals that occurs in the endoplasmic reticulum of the liver and kidney, it is the oxidation of the ω carbon—the carbon most far from the carboxyl group (in contrast to 
  
    
      
        β
      
    
    {\displaystyle \beta }
   oxidation which occurs at the carboxyl end of fatty acid, in the mitochondria). Physiological effects
As an example of normal synthesis, a 70 kilograms (150 lb) person would produce 11–34 mg of carnitine per day. Adults eating mixed diets of red meat and other animal products ingest some 60–180 mg of carnitine per day, while vegans consume about 10–12 mg per day. Most (54–86%) carnitine obtained from the diet is absorbed in the small intestine before entering the blood.