Increasing energy production helps sperm motility, which is why the same nutrients used to help your heart also help power up your sperm.
For a sperm to fertilize an egg, the sperm must swim to the woman's egg. But sperm that don't move very well aren't as likely to succeed. Their chances of reaching the egg to start a pregnancy are diminished.
In this study, 30 men (average age was 34) with fertility problems were diagnosed with decreased sperm motility. For three months, the men took a placebo. Then they took 2 grams of L-carnitine supplements orally every day for three months. After that, the men didn't take anything for another three months.
Semen samples were taken four times: at the study's start, after taking the placebo for three months, after taking carnitine for three months, and three months after therapy ended.
Sperm motility improved while the men took the carnitine supplements. The placebo didn't help at all. Meat, poultry, fish, and dairy products are the richest sources of L-carnitine. Wheat and avocados contain some L-carnitine, while fruits, vegetables, and grains contain little. It is best to use the Acetyl-L-Carnitine form with it. I recommend Acetyl-L-Carnitine 1,000 mg/day plus Carnitine 1,000 mg/day.
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Garolla, Fertility and Sterility, February 2005; vol 83: pp 355-361. Reuters Health.