Unpacking the Delhi Paradox: Seasonal drivers of sperm DNA fragmentation

Capsule Summary The paradox of improved semen quality despite peak winter pollution suggests that climate and air pollution interact in complex ways to influence sperm DNA integrity. Objective Male infertility is influenced by environmental and climatic factors. In Delhi/National Capital Region (NCR), air pollution levels vary markedly across seasons, with winter consistently recording the highest Air Quality Index (AQI). However, evidence on the combined impact of seasonality, air pollution, and climate on sperm DNA fragmentation index (DFI) in Indian men remains limited. Design Retrospective single-centre cohort study at a tertiary care in vitro fertilisation (IVF) unit in New Delhi, India (January 2016–January 2026). Subjects 217 men who underwent sperm DNA fragmentation assessment (Sperm Chromatin Dispersion assay) during the time period. Exposure Records were categorised by Indian Meteorological Department season (winter, pre-monsoon, monsoon, post-monsoon), with corresponding AQI, temperature, and humidity data from the Central Pollution Control Board. Statistical analysis using SPSS v25; significance set at p<0.05. Lag-adjusted (~90-day) and multivariable regression analyses captured exposure during spermatogenesis. Main Outcome Measures Association between seasonal variation, Air Quality Index (AQI), temperature, and humidity with sperm DNA fragmentation index (DFI) and conventional semen parameters. Results DFI showed the greatest seasonal variation (p=0.009), lowest in winter {median 27.75% (IQR 20.62-37.62); mean 28.67±10.43%} and pre-monsoon {median 25.50% (IQR 19.50-31.00); mean 27.59±11.83%}, rising through post-monsoon {median 31.00% (IQR 23.50-42.50); mean 35.02±18.92%} to peak in the hottest monsoon months {median 32.25% (IQR 24.50-45.50); mean 38.06±19.87%}. The proportion of men with very poor DFI (>50%) increased progressively from 1.5% in winter to 18.0% in monsoon (p=0.004). Despite winter having the highest AQI, it showed the most favourable DFI and better semen parameters (count, motility, morphology), while the hottest months showed the poorest outcomes — the “Delhi pollution paradox.” This inverse AQI-DFI association persisted after lag-adjustment (rho=-0.24, p=0.0005) and multivariable regression (β=-0.06, p<0.001), while lag-adjusted temperature correlated positively with DFI (rho=0.22, p=0.001) and remained an independent predictor in single-exposure regression (β=0.38, p=0.012). Contemporaneous temperature also correlated with poorer sperm morphology (rho=-0.18, p=0.008), and men with asthenozoospermia were exposed to significantly higher ambient temperatures than those with normal motility (26.33±6.75°C vs. 23.95±7.06°C; p=0.014). Humidity showed only a modest association with progressive motility (p=0.029). Elevated DFI was consistently associated with poorer semen quality, including asthenozoospermia, teratozoospermia, and oligospermia (all p≤0.001), and a lower total motile sperm count (p=0.017). Conclusion Seasonal and environmental factors significantly influence semen quality and sperm DNA integrity in men referred for DFI testing at a tertiary IVF centre in New Delhi, with better semen quality and lower DFI during cooler months. The paradoxically favourable semen parameters during Delhi’s most polluted winter months, despite markedly higher AQI, suggest a complex, non-linear interplay between climatic, environmental, and potentially host-related biological factors extending beyond contemporaneous air pollution exposure alone.