Heat and Mental Health - PART 2

Inclusion Criteria: * 18 ≥ age ≤ 25 at time of consent * has current depression as measured by a PHQ-9 score \>9 and corroborated by the DIAMOND Diagnostic Interview * resides within 75 mi. of Yale Biobehavioral Laboratory * willing/able to travel up to 75 mi. each way by car from their home to the Yale Biobehavioral Laboratory and back to their home * speaks/reads English fluently (surveys, interviews, and study measures are only validated in English; translating materials without proper validation could lead to responses that are not truly comparable, threatening reliability; limitations in budget, staffing, and available interpreters prevent the use of translated materials or hiring sufficient bilingual team members) * any gender * any race/ethnicity * able (have capacity)/willing to sign informed consent form (ICF) * has reliable access to a smartphone Exclusion Criteria: * age \<18 or age ≥26 at time of consent * does not have current depression as indicated by a PHQ-9 score \<9 * does not reside within 75 mi. of Yale Biobehavioral Laboratory * not willing/able to travel up to 75 mi. each way by car from their home to the Yale Biobehavioral Laboratory and back to their home * does not speak/read English fluently * unable (not have capacity)/unwilling to sign informed consent form (ICF) * has a job that requires rotating shifts and/or works 2nd or 3rd shift (i.e., night shifts) that affect circadian rhythm and sleep architecture * planned air travel between time zones during the study period that is likely to affect circadian rhythm * does not have reliable access to a smartphone * is pregnant or lactating * has a recent history (hospital admission within 2 years) of heat-related illness (e.g. heat stroke, heat exhaustion, or rhabdomyolysis) * weight \< 40 kg (88 lbs) - minimum body weight requirement * has a motility disorder of the gastrointestinal tract * has undergone surgical procedures in the gastrointestinal tract * has known swallowing disorders or dysphagia * has any condition that affects normal digestive function (GERD requiring treatment; Barrett's esophagus; achalasia or esophageal stricture; gastroparesis; IBS; inflammatory bowel disease (Crohn's disease or ulcerative colitis); celiac disease; microscopic colitis; chronic constipation or chronic diarrhea; malabsorption syndromes (e.g., pancreatic insufficiency, bile acid malabsorption); chronic liver disease; chronic pancreatitis; symptomatic gallbladder or post-cholecystectomy syndrome; prior bariatric surgery or bowel resection with ongoing effects; ostomy; chronic motility disorders; diabetes with autonomic neuropathy; neurologic or systemic diseases affecting GI function (e.g., Parkinson's disease, multiple sclerosis, scleroderma); chronic medication-induced GI dysfunction; eating disorders affecting digestion or nutrition. * has any condition that affects the body's ability to regulate temperature, including, Neurological conditions (such as spinal cord injuries, multiple sclerosis, traumatic brain injury, Guillain-Barré syndrome); Endocrine/metabolic disorders (such as hyperthyroidism/hypothyroidism, Type 1 or 2 diabetes, and anorexia nervosa); Cardiovascular conditions (such as Reynaud's disease, hypertrophic cardiomyopathy, and congenital heart); Dermatological conditions, (such as anhidrosis or hyperhidrosis and extensive burns or scarring associated with trauma). * engage in regular alcohol use (\>2 drinks per day), daily cannabis use, or any illicit drug use which can affect sleep architecture