# High intensity interval training and vitamin D3 supplementation in overweight and obese adults PMID: 29707918 Journal: Physiological Reports Published: 2018-05 Authors: Lithgow HM, Florida-James G, Leggate M ## Question Does vitamin D3 supplementation augment glycemic, cardiometabolic, and fitness adaptations to 6 weeks of HIIT in overweight and obese adults? ## Summary In overweight and obese but otherwise healthy adults, 6 weeks of supervised cycling HIIT improved aerobic fitness, waist/hip measures, systolic blood pressure, triglycerides, and glucose and insulin responses during an oral glucose tolerance test. Daily vitamin D3 corrected low vitamin D status but did not add metabolic benefit and appeared to blunt the glucose AUC improvement. ## Population - Overweight or obese Caucasian adults, otherwise healthy and recreationally inactive/lightly active - Sample size: 20 - Age: 19-45 years; completers 34 +/- 9 years - Sex: 14 male, 6 female - Fitness level: No more than two light-to-moderate exercise bouts per week - Health status: BMI 27-35 kg/m2; low baseline vitamin D; no diabetes reported ## Methodology - Randomized, double-blind, placebo-controlled supplementation trial with all participants completing supervised HIIT - 6 weeks - Supervised laboratory cycling sessions - Randomized and controlled study design. ## Protocol - 6-week cycling HIIT plus vitamin D3 or placebo. - Modality: Stationary cycling. - Work intervals: 1 minute. - Recovery: 1 minute active recovery at 50 W. - Sets or repetitions: 10 intervals per session. - Intensity: 100% VO2peak workload for sessions 1-6, 110% for sessions 7-12, 120% for sessions 13-18. - Session duration: 30 minutes including 5-minute warm-up and 5-minute cool-down. - Frequency: 3 sessions per week. - Program length: 6 weeks; 18 sessions. - Progression: Workload progressed every 6 sessions from 100% to 120% VO2peak workload. - Vitamin D3 versus placebo during same HIIT. - Modality: Same cycling HIIT in both groups. - Work intervals: Same as intervention. - Recovery: Same as intervention. - Sets or repetitions: Same as intervention. - Intensity: Same as intervention. - Session duration: Same as intervention. - Frequency: Same as intervention. - Program length: 6 weeks. - Progression: Same as intervention; supplement comparison was vitamin D3 100 micrograms/day versus placebo. ## Outcomes ### VO2peak Status: improved VO2peak increased by 12% and peak power increased by 17% across participants, without added effect of vitamin D3. VO2peak P < 0.001; peak power P < 0.001 ### OGTT glucose Status: mixed Glucose AUC improved overall, but the improvement occurred mainly in placebo and was attenuated in the vitamin D3 group. Glucose AUC 829 +/- 110 to 786 +/- 139 mmol h/L, P = 0.043; group x time interaction P = 0.035 ### OGTT insulin Status: improved Insulin AUC decreased after HIIT. 8101 +/- 4755 to 7024 +/- 4489, P = 0.049 ### Triglycerides Status: improved Triglycerides decreased after the intervention. 1.93 +/- 1.06 to 1.72 +/- 1.04, P = 0.025 ### Blood pressure Status: improved Systolic blood pressure decreased by about 6 mmHg. P = 0.004 ## Practical Insights - A 10 x 1-minute cycling format with equal active recovery was feasible under supervision in overweight/obese adults. - Progressing from 100% to 120% of VO2peak workload produced fitness and cardiometabolic changes over 6 weeks. - Vitamin D3 supplementation should not be presented as an enhancer of HIIT glycemic adaptations based on this small trial. ## Limitations - Small sample size and limited power for subgroup or interaction effects. - All participants exercised, so HIIT effects are primarily pre-post rather than compared with a non-exercise control. - Diet was not tightly controlled or monitored. - Post-testing 72 hours after the final session may miss acute exercise effects. ## Safety And Adherence - No adverse events or injuries were reported in the article. Safety/context details reported: participants were otherwise healthy and screened by exclusions, HIIT was supervised with HR and RPE monitoring, 20/22 completed, 2 withdrew for time commitments, HIIT adherence was 99.4%, and supplement/placebo compliance was 100%. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/29707918/) (pubmed) - [DOI](https://doi.org/10.14814/phy2.13684) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5925425/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.