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).  Now that I am back on the east coast living in a place where there are seasons (North Carolina), I am again struggling with increased insulin needs during the darker colder winter months.

Do blood sugars rise in the winter?

Although, I didn’t see any research that used continuous glucose monitoring to test this, there is quite a bit of  research suggesting that HbA1c levels (Hemoglobin A1c, generally accepted as a 3-month average of blood glucose 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)  Like most studies done in humans, there exists quite a bit of variability (shocker) meaning that not all participants had higher HbA1c levels in the winter.  Interestingly, in addition to higher HbA1c levels during the winter months, it appears that the winter months are also correlated with more new diagnoses of type 1 diabetes.(8)  There are a couple of hypotheses for this observed seasonal trend in HbA1c levels including: variation in hormones, vitamin D levels, and illness.

Cold Response

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.

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

Normal body temperature can range from 36.5–37.5 °C (97.7–99.5 °F).  So, when the body is cold, the hypothalamus (part of your brain) 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.(1)(3)

Vasomotor and Metabolic Response to Cold

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)  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.

Cortisol stimulates gluconeogenesis (the formation of glucose in the liver) 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 caused increased serum cortisol levels.(5)  Other studies have suggested that cortisol production is lower in the winter months, but plasma cortisol and tissue sensitivity are higher in winter.(4)  Studies on prolonged exposure to cold and darkness showed elevated cortisol, at least in about half of participants studied.(5)

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 exposure to cold environments caused a rapid increase in secretion of glucagon, potentially related to increased norepinephrine and cortisol levels.(5) (6)

 T3/T4: Long term exposure to cold air may increase consumption of the thyroid hormones T3 and T4, resulting in lower levels of T3 and T4.(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 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)