Objective: To measure folate levels in seminal plasma from smokers and nonsmokers and to evaluate relationships between seminal plasma folate levels and both folate nutriture and semen quality measures.
Design: Observational study.
Setting: United States Department of Agriculture, Western Human Nutrition Research Center, Presidio of San Francisco, San Francisco, California.
Patient(s): Healthy male smokers (n=24) and nonsmokers (n=24).
Main outcome measure(s): Blood levels of plasma folate and homocysteine, seminal plasma total, non-methyl- and 5-methyltetrahydrofolate concentrations, and total sperm count and density.
Results: Total seminal plasma folate concentrations were on average 1.5 times higher than blood plasma folate concentrations in all men. Seminal plasma folates contained 5-methyltetrahyrdofolate (74% of total) and non-methyltetrahydrofolates (26% of total); all samples had less than four glutamyl residues. Total and 5-methyltetrahydrofolate concentrations correlated significantly with blood plasma folate and homocysteine concentrations. Seminal plasma non-methyltetrahydrofolate levels correlated significantly with sperm density and total sperm count. Seminal plasma of smokers contained a proportionally lower concentration of non-methyltetrahydrofolates compared with nonsmokers.
Conclusion(s): Seminal plasma total folate and 5-methyltetrahydrofolate concentrations reflect folate nutriture. The non-methyltetrahydrofolate fraction of seminal plasma may be important for male reproductive function.