There’s no doubt about it: It’s not easy to manage your blood sugar levels during exercise. Physical activity is incredibly important to your overall health, but it creates all sorts of challenges during (and after) your workout. Keeping those levels steady takes experimentation with so many variables, including your nutrition, your insulin usage, and your type of exercise.
And guess what? Women have it even tougher, because the menstrual cycle causes hormonal changes that regularly change how sensitive you are to insulin. Of course we do (pardon me as I shake my head at adding yet another variable to the mix). It’s just one more variable making exercise just that much more difficult to manage.
There is little research on the subject, so it’s not surprising that not all women with type 1 diabetes realize how these factors interact, according to Jane Yardley, an associate professor of Physical Education at the University of Alberta.
“A lot of women aren’t aware of this, especially the newly diagnosed or teenage girls, who have a lot of other stuff going on.”
Dr, Yardley has devoted much of her career to the study of exercise in people with type 1 diabetes. She spoke to Diabetes Daily about the difficulty of managing glucose levels during and after exercise and the special challenges that women have to deal with.
Insulin on Board
If there’s one thing Yardley wants to stress, it’s that the insulin we administer with syringes, pens, and pumps is fundamentally different from the insulin made by a healthy body, and that this fact has big consequences for exercise.
“Most people don’t understand the difference between real insulin that’s made by the body and synthetic insulin. That’s the big problem with exercise. Synthetic insulin stays in circulation for several hours. Endogenous insulin has a half-life of five minutes. When someone without diabetes starts moving, the nervous system talks to the pancreas, and the amount of insulin being produced drops drastically. Within five minutes, there’s a huge decrease in the amount of insulin in circulation.
“In order to mimic that, people with type 1 diabetes have to plan 90 minutes to two hours in advance for exercise. This doesn’t necessarily get taught very well.”
The Menstrual Cycle
Women commonly experience shifting levels of insulin resistance during their monthly cycles.
“We see, from several studies, that probably around two-thirds of women with type 1 diabetes experience insulin resistance within the luteal phase, which gets worse as the cycle goes on. Usually that last week before the period is where we see the most insulin resistance.”
That insulin resistance can then rapidly disappear. Many women report that they have to battle hypoglycemia during the first few days of their next cycle — that’s likely because their insulin sensitivity has once again peaked, and they don’t realize that they’re using more insulin than they really need.
“The women that I’ve met who are the most in tune with their cycles are acutely aware of these fluctuations. Women I’ve met who are on the pump use different basal rates throughout the month.”
The only way to really figure this out for yourself is to experiment:
“Track your cycles. Try and figure out if you have higher insulin needs during that last week of the cycle before the period starts. If you do, be aware that any extra insulin on board when you start exercise could lead to a faster drop in blood glucose levels. You have to be more aware of having those extra carbs with you in that last week of the cycle.”
Paying close attention to the calendar and to signs of ovulation can help to accurately predict when you might need insulin adjustments. There are numerous apps and other methods for tracking your cycle to help determine when ovulation occurs. Documenting blood glucose trends throughout the month to help determine your optimal timeline for making insulin dosing adjustments. When you start tracking, you might be surprised just how much your hormones impact your day-to-day blood glucose levels.
Getting your insulin usage dialed in can really help preserve your reproductive health, according to Yardley:
“With both higher doses of insulin and hyperglycemia, we see more of an effect on the menstrual cycle. Polycystic ovary syndrome (PCOS) is way more common in type 1. Girls with type 1 usually start their period later, and menopause is usually a couple of years earlier. But if you’ve been able to keep your glucose levels in range, there are fewer problems.”
Puberty and Perimenopause
All of this is even trickier, however, at the beginning and end of the reproductive lifespan.
During puberty, girls with type 1 diabetes have many new variables to deal with. Girls experience more insulin resistance during puberty, and are also far more likely than boys to experience mental health issues. “All of these things can actually wreak havoc on your metabolism,” Yardley says.
At the other end of the reproductive lifespan it can be almost impossible to plan ahead during the menopausal transition, which brings erratic hormonal changes: “In perimenopause, it’s really screwy. Estrogen fluctuations change how the body manages glucose. Because those are completely unpredictable — you can go months without a period — it’s very hard.” Perimenopause is rarely spoken about and is just now finally getting the attention it needs and deserves. It can be an extraordinarily difficult time to manage diabetes and is worth discussing with your care team.
Insulin Management and Exercise
Most of us understand the fundamentals of how exercise impacts blood sugar. To put it very simply, exercise, especially cardiovascular exercise, often results in blood sugar lows (hypoglycemia). The underlying science is pretty simple: When you’re working out, you need more energy, and your body’s cells will greedily take up the glucose in your blood. One way to manage this is to eat more carbohydrates, adding more glucose to your system. Another is to reduce the amount of insulin in your body, which is much easier to do if you’re using an insulin pump.
Yardley insists that optimal insulin management for exercise starts as early as two hours before the workout — a point at which insulin pump users might want to reduce their basal rates.
The best way to avoid glucose issues may be to exercise first thing in the morning, before eating, and, most importantly, before using any bolus insulin.
“Fasting is a trick that is underutilized. If you’re an early bird, fasted exercise is probably the safest thing you can do. Because you have the lowest amount of insulin in circulation, and the body is releasing other hormones that cause blood sugar to rise, fasted exercise usually makes the glucose levels go up instead of down, and if they do go down, they go down a lot less.”
If you’ve turned your basal insulin rate down to avoid hypos during exercise, or stopped it entirely, you might want to turn it back up before you complete your workout.
“What we see with aerobic activity is that when you finish the activity, you get a big increase in glucose for two to three hours after.
“The main source of fuel for aerobic exercise is fat. The body will release fat at the same rate that the muscles need to use it. Once you stop exercising, the body takes a little while to respond, so it’s still releasing fat for a little while, which means you get a buildup of free fatty acids in circulation. This creates insulin resistance, and you need more insulin to maintain the same glucose levels.
“A lot of people in the exercise community with type 1 diabetes have picked up on this, and restart their basal before they stop exercising.”
Optimal insulin management doesn’t stop after the workout ends, Yardley says.
“Really well-managed people, people who are really dialed in with exercise, when they exercise later in the day they’ll decrease their basal rates overnight [if they’re on a pump]. Which is what you really need to do, particularly if it’s a high-intensity exercise session. If you’re doing intervals or weight lifting, you’re using the stored glucose from your muscle and liver, and those need to be paid back, and it usually takes more than one meal to pay them back. Your risk of going low overnight will be higher, unless you take quite a bit of carbohydrate before you go to bed.”
“A lot of recommendations say you should decrease your basal by 10 percent overnight if you’ve done intense activity during the day.”
It’s a lot to take in. Given all of these complexities and variables — insulin on board, food, exercise type, time of day, and hormonal cycles — it can seem impossible to get blood sugar management during exercise right. Yardley has some advice:
“When it comes to finding the combination, you have to change one thing at a time. If you change multiple variables at once, you don’t know what change actually helped, or what was causing your problem in the first place. What we do as scientists is hold everything consistent except for just one variable. You need to approach your body as if it’s a science experiment.”
[Diabetes Daily senior editor Ross Wollen contributed to this report.]