Influence of sex and age on serum nitrite/nitrate concentration in healthy subjects.

Measurement of serum nitrite/nitrate (NOx) concentrations has been considered useful to estimate nitric oxide production in humans. However little is known about the physiologic range and the factors affecting serum NOx levels. The aim of this study was, thus, to investigate the influence of sex and age on serum NOx levels in healthy subjects. We selected 263 healthy subjects (118 women and 145 men, 20-69 y) from 505 consecutive subjects who received annual medical checkups at our hospital. Serum NOx levels were determined using an analyzer employing the Griess method. The linear regression analysis showed that NOx increased significantly according to age in women (r=0.22, P<0.05), but did not in men (P=NS). Women of the younger age group (<40 y) showed significantly lower NOx levels than men of the same age group (P<0.05), whereas there was no significant difference between men and women of the older age (> or =40 y). Then, to investigate whether menopause affects serum NOx levels, middle aged women (46-55 y) were selected. Multiple logistic regression analysis showed that menopause was an independent factor for increased serum NOx levels in middle aged women (r=0.4, P<0.05). These results suggest that the serum NOx concentration is affected by age in healthy women, possibly depending on menopausal state.