Hyperglycemia- A Cold Case

I spent three years living in Maine, where winters were so long and freezing that we jokingly referred to the area as the tundra.  Although it’s hard to beat the gorgeous change of seasons in Maine, as you can imagine, the winters were shocking for a girl born and raised in Southern California.  I struggled not only to stay warm and avoid falling flat on my face every time I walked to class, but also to keep my blood sugars under control (not an easy task).

Have you ever wondered why winter seems to throw your blood sugars off?

Or maybe you don’t see a difference; however, research suggests that in general HbA1c levels tend to be higher in the cooler months and lower in the warmer months, and this trend appears to exist in both the northern and southern hemispheres. (2)  It’s been over five years since I left Maine, and now that I am living on the east coast again, I have decided to take a look into why type 1 diabetes is so much harder to deal with in the winter.  Like most diabetes mysteries, it all boils (or shall I say cools) down to physiology.
There are many complex mechanisms (some of which are still not well-understood) that may influence how your body responds to cold and may determine the extent of the response you experience.  In fact, there is actually a limited amount of information on type 1 diabetes and cold exposure, but I’ll do my best to summarize some of the research we do have.
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Maine in November

Body temperature is a balance of internal heat production and heat transfers between the body and the environment.

This is represented by a rather crazy biophysical equation that I won’t bore you with, but basically the fundamental idea is that the rate of body heat storage is determined by the summation of metabolic heat production (increased during physical activity or shivering), dry heat exchange (has to do with adjustments in blood flow), and evaporative heat loss (sweat). (1)(3)

Normal body temperature can range from 36.5–37.5 °C (97.7–99.5 °F).  So, when the body is cold, the hypothalamus signals to constrict peripheral blood vessels, minimize sweat production, and increase metabolic heat production (known as thermogenesis).  This response works to prevent dangerous drops in core temperature.

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How your body responds:

1. Vasomotor Response

Vasomotor responses reduce dry heat loss to the environment.  The body does this by peripheral vasoconstriction or decreasing blood flow to the periphery of the body by constricting the blood vessels.  This reduces heat transfer between the core and the skin/fat/subcutaneous muscle which helps insulate the internal organs, meaning that it minimizes heat loss.  It is hypothesized that this might be slightly impaired in patients with type I diabetes leaving individuals with type 1 at slightly greater risk of injury during cold exposure; however, there have been no studies that have directly examined this.(3)

2. Metabolic Response

 Shivering and non-shivering (mediated by that helpful brown fat) thermogenesis works to actually increase heat production.  Shivering employs the skeletal muscles, which have the greatest capacity of any body tissue to increase the rate of metabolism, increasing heat production.

3. Hormones and Neurotransmitters

Cortisol is secreted in response to stressful situations, so it would be logical that cortisol might be released when you’re exposed to a cold environment.  It is well known that cortisol stimulates gluconeogenesis (the formation of glucose) along with increasing vascular tone and suppressing the immune system.  A number of studies have suggested that short-term (an hour or two) exposure to cold environments cause an increase in serum cortisol levels.(5)  Other studies have suggested that cortisol production rate is lower in the winter months, but plasma cortisol and tissue sensitivity to glucocorticoids are higher in winter.(4)  Studies on prolonged exposure to cold and darkness also indicate elevated levels of cortisol, at least in about half of participants studied.(5)
Norepinephrine:
Also, part of that stress response, the catecholamine norepinephrine also known as noradrenaline has been shown to increase in response to both short-term and extended exposure to cold. (5)
Glucagon:
According to one study conducted in 1981, exposure to cold environments caused a rapid increase in secretion of glucagon.(5) (6)
 T3/T4:
Research suggests that long term exposure to cold air may increase consumption of the thyroid hormones T3 and T4, resulting in lower levels of T3 and T4, which may be related to some of the mood disturbances associated with living in cold climates.(5)
Growth Hormone:
Interestingly enough, exposure to cold environments appears to have no impact on growth hormone in a number of studies.  (5)(7)
How Hormones Might affect blood

How this might affect BG in Cold environments

It is currently thought that the increased HbA1c during the winter months in colder environments is primarily related to increases in plasma cortisol levels along with greater glucocorticoid responsiveness, which together results in lower insulin sensitivity.(3) (4)   As many type 1s will tell you, stress is not the best for blood sugars, so understanding the hormone changes that come in the winter months may help give type 1 diabetics better treatment options.

5 Tips for Better Control in the Winter

  1. Stay active.
  2. Stay warm.
  3. Keep monitoring your blood sugars.
  4. Work with your physician to adjust your basal rates if necessary.
  5. Consider trying mindfulness meditation (Shown in a number of studies to decrease serum cortisol)

 

 

On Hormones and Insulin Sensitivity:
Growth Hormone:
Epinephrine:
Norepinephrine:
Thyroid Hormones:
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