By Brittany Trout and Lana Sorrell, EMT, DMT
When it comes to fitness for diving, the recommendations for male and female divers are largely the same: good exercise tolerance, a healthy weight and awareness of possible concerns related to medical conditions and medications. Regardless of sex, all divers should use appropriate thermal protection, remain hydrated, understand the diving environment and dive conservatively.
Men and women, however, are physically and physiologically different. With women representing about a third of the recreational diving population – in 2013 the Professional Association of Diving Instructors (PADI) reported its population of certified divers as 66 percent male and 34 percent female, and males represent 64 percent of insured DAN members1 – it is important to consider specific health concerns that female divers face.
For both men and women, body temperature is centrally controlled in the hypothalamus and is affected by factors such as body fat content, fat distribution and body surface-area-to-mass ratio. Hormonal differences may affect thermoregulation, but body composition and size typically drive responses to cold exposure. Total heat loss may be greater in women because they generally have higher surface-area-to-volume ratios and lower muscle mass compared with men (greater muscle mass is associated with greater metabolic heat production). Some research suggests that women’s body temperature falls more rapidly during immersion in cold water while at rest. The bottom line is that every diver should wear a suit that fits well and keeps him or her warm – exposure protection helps compensate for any heat loss due to hormonal or anthropometric differences.
No evidence suggests that women who dive while menstruating are harassed or bitten by sharks more often. However, anxiety, dizziness, feeling cold and the potential for panic may be exaggerated during menstruation or premenstrual syndrome (PMS). Temporary iron deficiency during menstruation may reduce exercise capacity, so women should be prepared to modify their diving behaviour if necessary. Menstruation can trigger migraines, which are more common in women than men. Delay diving if migraine symptoms occur.
Research suggests there may be a slight increase in risk for decompression illness during the follicular stage of the menstrual cycle (the roughly two-week span preceding ovulation). Everyone should dive within established limits, but women might consider reducing their diving exposure during the follicular stage by incorporating additional conservatism into their dive plan. Completely refraining from diving while menstruating is not necessary, but women should be aware of how PMS and menstruation affects them and whether emotional stress, irritability, cramping, headaches or associated symptoms might compromise dive safety.
Use of oral contraceptives (as well as a sedentary lifestyle and long-distance travel) may contribute to possible clot formation such as deep vein thrombosis. Research indicates that oral contraceptive pill (OCP) use can increase the risk of a thromboembolic event such as a pulmonary embolism, heart attack or stroke. A 1985 report showed that women who use OCPs and smoke more than 25 cigarettes per day have a 23-fold increased risk for a thromboembolic event compared with those who do not smoke.5 While a thromboembolic event may be at least somewhat manageable on dry land, it would be unmanageable in the water. Quitting smoking, exercising regularly and moving frequently during long trips can help minimise the risk of an emergency due to clot formation.
Not only should pregnant women refrain from diving, women who think they may be pregnant or are trying to become pregnant should likewise avoid it. For ethical reasons, there has never been experimental research investigating the effects of diving on a foetus. The retrospective anecdotal data regarding pregnancy and diving shows there may be a risk to the foetus should a mother continue diving during pregnancy. A survey of 208 mothers who dived during pregnancy showed higher rates
of low birth weight, birth defects, neonatal respiratory difficulties and other problems.2 Decompression studies conducted on sheep demonstrated that a foetus may develop bubbles before the mother displays clinical symptoms of decompression sickness.3,4 (Sheep studies are relevant because the placentas of sheep and humans are similar.) The foetus runs the potential risk of death because the foetal cardiovascular system has no effective filter. Therefore, any bubbles formed are likely to go directly to the brain and coronary arteries. All sheep studies showed very high rates of foetal loss. Although it is limited, the available data seem to suggest strongly that women should refrain from diving while pregnant or trying to conceive.