Supplements of L-carnitine, a vitamin-like substance that occurs naturally in the body, have previously been shown to improve fertility.
The new study was designed to explore further carnitine's role in fertility.
Researchers at the University of Padova divided 30 men with asthenozoospermia into two groups depending on whether they had normal or abnormal mitochondria function. Mitochondria provide the energy needed for sperm to move and are therefore crucial to carnitine's benefit.
The groups took a placebo for three months and then 2g of oral L-carnitine each day for a further three months.
In patients with normal mitochondria function, movement rose from 29.3 per cent before treatment to 41.1 per cent after three months of carnitine. However, in those with abnormal function, movement held steady at about 24 per cent, report the authors in the February issue of Fertility & Sterility (vol 83, issue 2, pp355-61).
They concluded that "carnitine treatment might improve sperm motility in the presence of normal mitochondrial function".
L-carnitine is currently marketed mainly for heart health and for post-exercise recovery. The new findings suggest the potential for a new target for supplement makers.