ObjectiveTo determine the effect of prolonged exposure to a submarine environment on biomarkers of cardiometabolic risk in Royal Navy (RN) submariners.MethodsSerum lipids (cholesterol (C), triglyceride (TG), low-density lipoprotein cholesterol, high-density lipoprotein cholesterol (HDL-C), non-HDL-C), glucose, insulin and anthropometrics were compared within three RN submarine crews before and after submerged patrols of 12 or 6 weeks, and with a crew that remained ashore (SUB-HOME). Dietary intake and activity patterns were self-reported during each patrol. Differences were assessed in crew characteristics using one-way analysis of variance and in serum lipids using paired t-tests.ResultsPostpatrol, the mean body weight of submerged crews decreased (−1.4±4.2 kg, p=0.0001), but increased in SUB-HOME (1.9±1.8 kg, p=0.0001). Modest improvements in serum lipids (mean individual change (mmol/L); C=−0.3±0.7, p=0.0001; TG=−0.3±0.7, p=0.0001; HDL-C=−0.1±0.3, p=0.0001; non-HDL-C=−0.2±0.6, p=0.012), glucose (−0.2±0.5, p=0.0001) and insulin (−1.5±4.6 mU/L, p=0.001) were observed in submerged crews. Changes in serum lipids were positively associated with changes in body weight within crews combined. Energy intake was maintained during submerged patrols but was lower compared with non-submerged (11 139±2792 vs. 9617±2466 kJ, p=0.001; 11 062±2775 vs. 9632±2682 kJ, p=0.003).ConclusionsThe environment of a submerged submarine produced no adverse effects on serum biomarkers of cardiometabolic risk in crew. Conversely, modest improvements in these biomarkers were associated with a decrease in body weight.