Background and objectives: Vitamin D and folate are highly UV sensitive, and critical for maintaining health throughout the lifecycle. This study examines whether solar irradiance during the first trimester of pregnancy influences vitamin D receptor (VDR) and nuclear folate gene variant occurrence, and whether affected genes influence late-life biochemical/clinical phenotypes. Methodology: 228 subjects were examined for periconceptional exposure to solar irradiance, variation in vitamin D/folate genes (polymerase chain reaction (PCR)), dietary intake (food frequency questionnaire (FFQ)) and important adult biochemical/clinical phenotypes. Results: Periconceptional solar irradiance was associated with VDR-BsmI (P=0.0008 wk7), TaqI (P=0.0014 wk7) and EcoRV (P=0.0030 wk6) variant occurrence between post-conceptional weeks 6-8, a period when ossification begins. Similar effects were detected for other VDR gene polymorphisms. Periconceptional solar irradiance was also associated with 19 bp del-DHFR (P=0.0025 wk6), and to a lesser extent C1420T-SHMT (P=0.0249 wk6), a folate-critical time during embryogenesis. These same genes were associated with several late-life phenotypes: VDR-BsmI, TaqI and ApaI determined the relationship between dietary vitamin D and both insulin (P<0.0001/BB, 0.0007/tt and 0.0173/AA, respectively) and systolic blood pressure (P=0.0290/Bb, 0.0299/Tt and 0.0412/AA, respectively), making them important early and late in the lifecycle. While these and other phenotype associations were found for the VDR variants, folate polymorphism associations in later-life were limited to C1420TSHMT (P=0.0037 and 0.0297 for fasting blood glucose and HbA1c levels, respectively). We additionally report nutrient-gene relationships with body mass index, thiol/folate metabolome, cognition, depression and hypertension. Furthermore, photoperiod at conception influenced occurrence of VDRTru9I and 2R3R-TS genotypes (P=0.0120 and 0.0360, respectively). Conclusions and implications: Findings identify environmental and nutritional agents that may interact to modify gene-phenotype relationships across the lifecycle, offering new insight into human ecology. This includes factors related to both disease aetiology and the evolution of skin pigmentation.