Religion and ethnicity interaction as a predictor of male fertility in Nigeria: Evidence from a national representative sample.

High fertility constitutes a challenge to men's health conditions in Nigeria, a low-income country. Religion and ethnicity are central to the current Male Fertility (MF) level in Nigeria. This study determined the relationship between Male Fertility (MF) and Religion Ethnic Interaction (REI) amidst other socio-demographic characteristics in Nigeria. Nigeria Demographic and Health Survey data, 2018 was used. Men aged 15-59 years [n = 8,786] were sampled using a multi-stage approach. Fertility was measured by the number of Children Ever Born (CEB). REI was generated using the combination of religion and ethnic groups; Hausa/Fulani Muslim, Igbo Christian, Yoruba Christian, and Yoruba Muslim. However, Hausa/Fulani Christians and Igbo Muslims were excluded from this study because a few men in these categories were available in the original sample. Weighted data were analyzed using the Negative Binomial (NB) model (α0.05). The mean age and CEB of the men were 32.9±12.0 years and 3.18±4.4 respectively. The mean CEB among men aged 45-59 years was highest among Hausa/Fulani Muslims (x = 11.57±5.98), but least among Yoruba Christians (x = 4.44±2.67). About 33.4% of the Hausa/Fulani Muslims had had ≥5 children, while 13.7% were reported among the Yoruba Christian men (p<0.001). The fertility Incidence Rate Ratio (IRR) was higher among Hausa/Fulani Muslims, but less among Igbo Christians, and Yoruba Christians than Yoruba Muslims. Restricting the analyzed data to only monogamous men revealed no significant differences in the fertility IRR of Yoruba Christians and Yoruba Muslims, but the fertility IRR was significantly higher among the Hausa/Fulani Muslims than Yoruba Muslims. A disparity exists in MF across the REI groups with the Hausa/Fulani Muslims being the major contributors to high MF. Therefore, bridging the gap in access to fertility control measures and programmes that might have resulted from religion and ethnic differences will reduce male fertility level in Nigeria.