Diabetes is a disease in which the body is unable to produce or effectively respond to insulin, a hormone the body needs in order to use glucose (sugar) in the blood. Healthy individuals maintain plasma glucose in a narrow range of 70 to 110 milligrams per deciliter (mg/dL) of blood. People with diabetes can experience dramatic fluctuations in plasma glucose. The primary concern is that low levels of blood glucose (hypoglycemia) can make you lose consciousness. Long-term elevation of blood glucose (hyperglycemia) can result in circulatory problems and compromised vision.
The inability to produce insulin is known as Type 1 diabetes, or insulin-requiring diabetes mellitus (IRDM). The inadequate production of insulin or the insensitivity of the body’s cells to insulin is known as Type 2 diabetes, or mature onset diabetes. Individuals with diabetes, particularly IRDM, have faced exclusion from activities during which a sudden loss of consciousness might pose a significant risk, such as scuba diving.
DAN Study on Plasma Glucose Levels and Recreational Diving
DAN researchers measured the plasma glucose response to recreational diving in adults with IRDM compared to a control group of divers without diabetes. The divers with IRDM had at least moderately controlled diabetes, no secondary complications and no hospitalizations for blood glucose irregularities in the previous 12 months; furthermore they understood the relationship between plasma glucose and exercise.
Most of the dives were from commercial liveaboard dive boats or day boats in subtropical or tropical waters. The divers’ blood glucose had to be above 80 mg/dL before each dive. Divers used commercially available portable monitors to measure plasma glucose by finger stick. Values were recorded several times before and after the dives.
Results
The variability in plasma glucose levels was higher in the IRDM group than in the control group. Neither group had symptoms or complications related to hypoglycemia during dives or immediately postdive, despite some low levels of plasma glucose. The IRDM divers took extra glucose before nearly half of the dives. Postdive plasma glucose fell below 70 mg/dL after 7 percent of the IRDM group dives (the lowest being 41 mg/dL) and after 1 percent of the control group dives (the lowest being 56 mg/dL).
Although IRDM divers did not report symptomatic hypoglycemia immediately before, during or immediately after diving, there were instances unrelated to diving. Symptoms included nausea, anxiety, shaking, feeling cold and headaches. In several cases, these symptoms were enough to wake the diver in the middle of the night. Moderate levels of asymptomatic hyperglycemia (greater than 300 mg/dL) were present on 67 occasions predive and 17 occasions postdive.
Conclusions
- Plasma glucose level changes in the IRDM divers ranged from a rise of 283 mg/dL to a fall of 370 mg/dL. The magnitude of change was frequently surprising to the divers, who had experience in diabetes management. People with less stable IRDM and those who regularly maintained very tight control may have an increased risk of hypoglycemia.
- High plasma glucose may increase susceptibility to decompression sickness or worsen neurological decompression illness.1 Simply elevating glucose levels to reduce the risk of hypoglycemia occurring during a dive may not be completely harmless.
- Despite occasional instances of plasma glucose levels in the 40 to 50 mg/dL range, the lack of symptoms associated with hypoglycemia in this study could be due to a failure to recognize or report symptoms. Divers noted and corrected equivalent low blood glucose levels they experienced at other times of the day.
- Signs and symptoms associated with hypo- or hyperglycemia can be due to other medical conditions, such as hypothermia, nausea from seasickness and possibly decompression illness.
- All of the dives monitored were recreational, with minimally or modestly stressful conditions in tropical or subtropical waters. The additional stress associated with additional or more complex equipment, more severe water conditions, more extreme dive profiles, or emergencies could produce more dramatic fluctuations in plasma glucose.
- This study had adult subjects only. Children may be at higher risk due to increased distractibility, less experience in regulating plasma glucose and a physiological predisposition to greater variability in plasma glucose levels during exercise.2
Diabetes and Diving Safely
- Symptoms of severe hypoglycemia include seizure and loss of consciousness, which are likely to be fatal if experienced underwater.
- There are no reliable ways to take a rest while diving as there are when exercising on land. Conditions may change rapidly and turn a relaxed dive in benign conditions into a physically demanding situation.
- Management of serious illnesses is more difficult in remote areas.
- The dive buddy standard assumes that both individuals can provide adequate and rapid support for a partner. If a preexisting medical condition impairs one of the pair, this assumption may not be accurate.
- Diabetes can be progressive, and such progression may increase risk while diving.
For more information, see Guidelines for Diabetes and Recreational Diving.
Neal W. Pollock, Ph.D., Donna M. Uguccioni, M.S., Guy de L Dear, M.B., FRCA
References
1. Moon RE. Fluid resuscitation, plasma glucose and body temperature control. In: Moon RE, ed. Report of the Decompression Illness Adjunctive Therapy Committee of the Undersea and Hyperbaric Medical Society; 2003; Duke University, Durham NC: Undersea and Hyperbaric Medical Society; 2003: 119-128.
2. American Diabetes Association. Diabetes Mellitus and Exercise. Diabetes Care 2002; 25(90001):S64-8.