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FFA. The increase in FFA coupled to the increase in T3 ob- The information contained herein sheds light on the acute
served in this effort is suggestive, again, of increased supply and short-term chronic effect of cold-water diving on the hor-
of fuel for thermogenesis if cold exposure persists. These data monal response. Despite core temperature stability, short-term
are in contrast to others who have measured a decrease in T3 cold-water submersion induced physiological shifts with some
with prolonged cold exposure (20–42 weeks) but in agreement hormones not resetting with a day of rest. While the sample
with some that have measured an increase when atmospheric is small, the data provide an important contribution to un-
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pressure is changed. The overall lack of change in T4 and derstanding the overall health and/or potential health risk for
TSH is in concurrence with other efforts that noted little to individuals exposed to extreme cold-water diving whether for
no change in T4 and TSH as in this effort. 26,42,43 Similarly, their occupation or recreationally. To date, there are ample
we measured no change in IGF-1 on day 1 similar to other data on head-out immersion but little to none on cold-water
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acute cold- water immersion efforts. However, by day 3, we full submersion with changes in hydrostatic pressure, which
noticed a significant decrease in IGF-1 as has been noted in occurs with depth achievable only with SCUBA.
cold exposed animals and during military training. 45–48 Nindl
et al. showed that IGF-1 was a good marker for increased Conclusion
48
stress due to heavy military training and caloric deficit. Unlike
previous work in a military environment, participants in this The present findings indicate that repeated cold-water diving
effort had not undergone arduous physical activity and were induces a SAM/SNS driven stress response with suppression of
not calorically deprived per se. However, recent work from HPA and hormones related to recovery and repair. Diurnally
our lab demonstrated an increase in energy expenditure during regulated hormones were unaffected by multiple cold-water
21
cold-water diving ; thus, while physical activity was low, the submersions, which may be a function of habituation to the
combination of activity with cold may have provoked a ca- cold. Nevertheless, little data exist on the impact of cold- water
loric deficit. Furthermore, IGF-1 is closely associated to sleep SCUBA, thermoregulation, and hormonal fluxes especially
restriction and nutritional deficiency. The decrease in IGF-1 by with a dual dive paradigm. While the sample size was too
day 3 could be indicative of poor sleep and inadequate nutri- small to determine the role of SAM/SNS, HPA, and thyroid
tional intake. The location of the training for this effort was hormone effect on thermoregulation, it addresses a gap in our
very remote, and there was no access to food (e.g., no grocery understanding of physiological adaptions that occurs in ex-
stores, vending machines) outside of the meal periods. While treme environments. Further, work is needed to fully elucidate
nutritional intake was not accounted for in this effort, it can be the acute stress response and thermometabolic adaptations
speculated that, by day 3, participants may have had some nu- during cold-water submersion.
tritional deficit due to the combination of diving and increased
metabolism due to the cold. Moreover, participants were in Funding
shared spaces for sleeping and out of their natural sleep hab- This work was supported by the Office of Navy Research
itat during this study, which may have impacted overall sleep under work unit no. N1506. The views expressed in this ar-
quantity and quality. Alternatively, changes in IGF-1 appear to ticle are those of the authors and do not necessarily reflect
be dependent on stress exposure time, with the previous de- the official policy or position of the Department of the Navy,
crease in plasma IGF-1 concentration occurring after days of Department of Defense, nor the U.S. Government. Carina M.
training. The observed decrease in IGF-1 noted in this study Pautz was supported by a predoctoral graduate student award
43
could be due to a culmination of factors related to sleep, cold, from Dornsife College at the University of Southern Califor-
caloric intake, and physical activity. nia. Lorraine P. Turcotte was supported by a research grant
from the University of Southern California Women in Science
and Engineering (WiSE) program.
Limitations
There are several limitations that need to be addressed. Primar- Conflicts of Interest
ily is the small sample size. These studies are very difficult to The authors have no conflicts of interest to declare.
conduct in the field, and the ratio of divers to support the safety
of personnel is high, which limits sample size. Moreover, all Availability of Data and Material
participants were Norwegian and, while not regularly engaged The datasets generated during and/or analyzed during the cur-
in cold-water diving, may be habituated to the cold. The out- rent study are available from the corresponding author upon
comes from this effort should be applied to those from cold re- receiving a reasonable request.
gions. Natural circadian rhythm may have influenced post-dive
values of diurnally regulated hormones; however, studies have Authors’ Contributions
shown that during physically and/or mentally intense train- KRK conceived and designed the experiments. CMP, AEJ, LJA,
ing programs, circadian rhythms for some hormones can be PAS, JM, and KRK performed the experimental work and col-
abolished. Nevertheless, plasma values of diurnally regulated lected the data. CMP, AEJ, LPT, and KRK were involved in
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hormones should be cautiously considered. Moreover, women sample analysis as well as data analysis and interpretation.
were not included in this effort as they were not assigned to the KRK, CMP, and LPT drafted the manuscript, and KRK revised
training; thus, the results from this effort can only be applied to the manuscript critically for intellectual content. All authors
the male population. Finally, this effort was conducted in elite approved the final version of the manuscript.
military divers, and thus results may only be relevant to a fit
population. Nutrition and caloric intake were not accounted Ethics Approval
for in this effort. All meals were taken together, and food choice The study protocol was approved by the Naval Health Re-
was limited to the meal that was provided at the dining facility; search Center Institutional Review Board in compliance with
thus, slight variations in intake and quantity of calories con- all applicable Federal regulations governing the protection of
sumed may have impacted some hormones in this effort. human subjects. Research data were derived from an approved

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