Caffeine intake is not associated with serum testosterone levels in adult men: cross-sectional findings from the NHANES 1999–2004 and 2011–2012

<p><b>Objective:</b> The association of caffeine intake with testosterone remains unclear. We evaluated the association of caffeine intake with serum testosterone among American men and determined whether this association varied by race/ethnicity and measurements of adiposity.</p> <p><b>Methods:</b> Data were analyzed for 2581 men (≥20 years old) who participated in the cycles of the NHANES 1999–2004 and 2011–2012, a cross-sectional study. Testosterone (ng/mL) was measured by immunoassay among men who participated in the morning examination session. We analyzed 24-h dietary recall data to estimate caffeine intake (mg/day). Multivariable weighted linear regression models were conducted.</p> <p><b>Results:</b> We identified no linear relationship between caffeine intake and testosterone levels in the total population, but there was a non-linear association (<i>p</i>_nonlinearity < .01). Similarly, stratified analysis showed nonlinear associations among Mexican-American and Non-Hispanic White men (<i>p</i>_nonlinearity ≤ .03 both) and only among men with waist circumference <102 cm and body mass index <25 kg/m² (<i>p</i>_nonlinearity < .01, both).</p> <p><b>Conclusion:</b> No linear association was identified between levels of caffeine intake and testosterone in US men, but we observed a non-linear association, including among racial/ethnic groups and measurements of adiposity in this cross-sectional study. These associations are warranted to be investigated in larger prospective studies.</p

Association of caffeine intake with erectile dysfunction among normal weight and overweight/obese men in NHANES 2001–2004.

<p>^†Adjusted for age, vigorous and moderate physical activity, smoking status, education, race/ethnicity, obesity (BMI ≥ 30 kg/m²), total water intake (plain and tap), total energy (continuous), alcohol (continuous). Error bars represent 95% confidence intervals. <i>P</i>_<i>trend</i><i>= 0</i>.<i>08 and P</i>_{<i>interaction</i>}<i>= 0</i>.<i>09</i>. ^*Erectile dysfunction was defined as “sometimes” or “never” able to maintain an erection for satisfactory sexual intercourse. ^‡ Approximately 170–375 mg/day of caffeine intake is equivalent to 2–3 cups of coffee. ^aOverweight/obesity = body mass index ≥ 25 kg/m².</p

Association of caffeine intake with erectile dysfunction in NHANES 2001–2004 (n = 3724).

<p>^†Adjusted for age, vigorous and moderate physical activity, smoking status, education, race/ethnicity, obesity (BMI ≥ 30 kg/m²), total water intake (plain and tap), total energy (continuous), alcohol (continuous). Error bars represent 95% confidence intervals. <i>P</i>_<i>trend</i><i>= 0</i>.<i>19</i>. ^*Erectile dysfunction was defined as “sometimes” or “never” able to maintain an erection for satisfactory sexual intercourse. ^‡Approximately 170–375 mg/day of caffeine intake is equivalent to 2–3 cups of coffee.</p

Association of caffeine intake with erectile dysfunction among men with and without diabetes in NHANES 2001–2004.

<p>^†Adjusted for age, vigorous and moderate physical activity, smoking status, education, race/ethnicity, obesity (BMI ≥ 30 kg/m²), total water intake (plain and tap), total energy (continuous), alcohol (continuous). Error bars represent 95% confidence intervals. <i>P</i>_<i>trend</i><i>= 0</i>.<i>57 and P</i>_{<i>interaction</i>}<i>= 0</i>.<i>65</i>. ^*Erectile dysfunction was defined as “sometimes” or “never” able to maintain an erection for satisfactory sexual intercourse. ^‡ Approximately 170–375 mg/day of caffeine intake is equivalent to 2–3 cups of coffee. ^aDiabetes = fasting plasma glucose ≥126 mg/dl, self-reported diagnosis, or medication treatment.</p

Association of caffeine intake with erectile dysfunction among men with and without hypertension in NHANES 2001–2004.

<p>^†Adjusted for age, vigorous and moderate physical activity, smoking status, education, race/ethnicity, obesity (BMI ≥ 30 kg/m²), total water intake (plain and tap), total energy (continuous), alcohol (continuous). Error bars represent 95% confidence intervals. <i>P</i>_<i>trend</i><i>= 0</i>.<i>13 and P</i>_{<i>interaction</i>}<i>= 0</i>.<i>30</i>. ^*Erectile dysfunction was defined as “sometimes” or “never” able to maintain an erection for satisfactory sexual intercourse. ^‡ Approximately 170–375 mg/day of caffeine intake is equivalent to 2–3 cups of coffee. ^aHypertension = systolic/diastolic blood pressure ≥140/90 mmHg, self-reported diagnosis, or medication treatment.</p

Description of the 47 meta-analyses where the respective most precise study had a nominally statistically significant effect.

<p>Description of the 47 meta-analyses where the respective most precise study had a nominally statistically significant effect.</p

Venn diagrams of the meta-analyses of animal studies of neurological disorders.

<p>We plotted the number of studies with a total sample size of at least 500 animals; those which showed a nominally (<i>p</i>≤0.05) statistically significant effect per fixed-effects synthesis; those that had no evidence of small-study effects; and those that had no evidence of excess significance. The numbers represent the studies that have two or more of the above characteristics according to the respective overlapping areas.</p

Observed and expected number of “positive” studies for all neurological diseases in subgroups.

<p>Observed and expected number of “positive” studies for all neurological diseases in subgroups.</p

The strongest associations between the pleiotropic SNPs and breast cancer risk.

a<p>OR = Odds Ratio.</p>b<p>95% CI = 95% Confidence Intervals.</p>c<p>All analysis were adjusted for age at diagnosis and in the BPC3 for cohort of provenience.</p

Description of the scoring system of the 10 dietary (and lifestyle) scores.

<p>Description of the scoring system of the 10 dietary (and lifestyle) scores.</p