Exercise and Diabetes Mellitus
Stan Reents, PharmD
08/02/2007 01:33 PM
Last Revision: 09/14/2013 06:55 PM
Diabetes, or, more specifically, diabetes mellitus, is a common disease. It is exists in 2 general types:
- Type-1: due to diminished output of insulin from the pancreas
- Type-2: due to diminished responsiveness of tissues to the actions of insulin
Type-2 makes up 90-95% of all cases of diabetes.
Quite frankly, this disease is out of control, both in the US, and worldwide. Consider the following statistics:
NOTE: Fasting blood sugar (blood glucose) is the medical test used to diagnose diabetes. When compiling prevalence statistics, previously, fasting blood glucose was the only parameter considered. However, the most recent National Diabetes Fact Sheet, 2011 from the CDC now also utilizes hemoglobin A1C.
DIABETES IN THE US
According to the CDC, in 2010, the number of Americans with diabetes (both diagnosed and undiagnosed) was 25.8 million, or, about 8.3% of the US population. Diabetes was listed as the 7th leading cause of death in the US (source: National Diabetes Fact Sheet, 2011).
(adults in the US)
|• Diabetes Mellitus
||> 125 mg%
||• diagnosed: 18.8 million
• undiagnosed: 7 million
TOTAL: 25.8 million
||100 - 125 mg%
By the year 2050, it is predicted that 48 million Americans will have diabetes.
• Diabetes in adults (ages 20 and up): 25.6 million, or 11.3% of this group, have diabetes. Roughly 1.3 million new cases are diagnosed per year in adults ages 20 years or older. Even worse, another 79 million adults (35%) have prediabetes, a condition that is considered to be the precursor to full-blown diabetes mellitus.
• Diabetes in children and adolescents: Because of its association with obesity and a sedentary lifestyle, type 2 diabetes used to be a disease that was only found in adults. It is now being seen in children and adolescents. According to the CDC's National Diabetes Fact Sheet, 2011, in 2010, 215,000 children and adolescents have diabetes. Worse, over 2.7 million have evidence of impaired glucose tolerance (Duncan GE. 2006).
• Diabetes in Native Americans: Most often, the cause of type-2 diabetes is lifestyle (ie., a combination of sedentary lifestyle with overeating, leading to obesity). However, genetic factors also play a role. As of April 2007, at least 10 genes involved in the development of diabetes have been identified in humans. A prime example is the prevalence of diabetes mellitus in Native Americans, particularly Pima Indians. In 2004, the rate of diabetes in American Indians and Alaskan Natives was 17.1%, substantially higher than the 8% prevalence in the general US population (Acton KJ, et al. 2006).
And if the stats listed above aren't depressing enough, then consider what is going on worldwide:
(source: Diabetes Atlas, 4th ed., published by the International Diabetes Federation)
In the fall of 2011, world population reached 7 billion. So, stated another way, about 5.2% of the entire world population has diabetes mellitus. It is estimated that, in 2011, one person dies from diabetes every 7 seconds.
In 2006, it was predicted that, by 2025, 380 million people worldwide -- or, approximately 7% of the world's population -- would have diabetes (Lindstrom J, et al. 2006.), however, the rate has increased since then; that estimate may now be too low. The World Health Organization already considers obesity and diabetes to be a global health crisis.
OBESITY LEADS TO DIABETES
Many people know that there is a relationship between obesity and diabetes, particularly, type-2 diabetes which makes up 90-95% of all cases.
Obesity, particularly if it occurs at an early age, is a strong risk factor for developing diabetes in later life. At the American Diabetes Association meeting in Washington DC (June 12, 2006), Dr. Venkat Narayan, head of epidemiology and statistics at the CDC's diabetes branch, presented a report based on survey data from over 800,000 healthy adults. He found that:
...the odds that a person who is a normal weight at age 18 yrs. will develop diabetes in later life are roughly 1-in-5, or 1-in-6. This is bad enough. But, "if you are very obese at age 18, the risk of developing diabetes rises to 3-in-4," he said.
Former Arkansas governor Mike Huckabee is an example of someone who developed type 2 diabetes as a complication of obesity:
In 2003, Governor Huckabee weighed 280 lbs. His BMI was 39, one unit shy of being categorized as "morbidly obese." At his height (5'11"), his weight should be no greater than 175 lbs (based on desirable BMI values).
Then, one day in March 2003, Huckabee developed numbness and tingling in his arm. His physician diagnosed diabetes.
Even professional athletes are not immune to the consequences of weight gain and a sedentary lifestyle. NBA hall of famer Dominique Wilkins discovered that first-hand. After he retired from the NBA, he put on about 25 pounds, and then was diagnosed with type-2 diabetes. He has since lost about 30 pounds, improved his diet, and resumed a more disciplined exercise routine, but still requires oral medication to control his diabetes. (His father suffered from type-1 diabetes.)
"TREATING" DIABETES WITH EXERCISE
People with diabetes know how important diet is to maintain good blood sugar control. But, fewer are clear on how beneficial exercise can be.
This is not surprising. Healthcare professionals often recommend "diet and exercise" for patients with diabetes. But, while the details regarding diet are clearly spelled out for diabetics, specific information regarding exercise is not. How much exercise? How often? And what type?
In 1972, Paula Harper, a registered nurse, was diagnosed with type-1 diabetes. She discovered that the medical profession offered very little help when she asked these questions. In fact, she says, "I was most often told not to do it or given inadequate or misleading advice." She subsequently developed her own training regimen and, within a year, entered her first marathon. She has since run dozens of marathons, and competed in other endurance races, such as triathlons, ultramarathons, and century bike races (Thurm U, et al. 1992).
In 1985, Harper founded the International Diabetic Athletes Association (IDAA), since renamed to "The Diabetes Exercise and Sports Association" (DESA) (see below).
Sadly, fifteen years later, the medical profession continued to discourage diabetic athletes from competition. A case in point is American swimmer Gary Hall, Jr: In 1999, he was diagnosed with diabetes mellitus. His doctor told him he wouldn't swim competitively. Fortunately, he didn't listen. At the 2004 Olympic Games in Athens, Hall won the men's 50-meter freestyle, thus earning the crown, "world's fastest swimmer."
But, in fact, for many people with type-2 diabetes, regular exercise can be highly effective.
The call to action for Mike Huckabee came in June 2003 when former Arkansas governor Frank White died of a heart attack. Over the next year, Huckabee changed his diet and began running. First, he reduced his daily intake from 3000 calories per day down to 800 calories per day, by eating meal replacement shakes and unlimited vegetables. After 3 months, his physician relaxed the diet to 1600 calories per day.
After he lost 40 lbs., exercise was added. Though tough at first, after 4 months, Huckabee could run 3-4 miles. By March 2004, he had lost 105 lbs. and all symptoms of diabetes have been reversed.
FOOTNOTE: Huckabee was profiled in a recent issue of Runner's World magazine. He ran his first 5-K race on July 4, 2004 and finished in 28:39 minutes. As of November 2006, he had run 3 marathons and was planning to run in the NYC Marathon. His most recent finish time was 4:26, in March 2006, at the Little Rock Marathon.
PHYSIOLOGIC ACTIONS OF EXERCISE IN DIABETES
To better understand the effects of exercise on glucose control, we need to separate this process into two parts: (a) the acute effects of exercise (ie., what happens during an exercise session and for several hours afterwards) and (b) the chronic effects of exercise (ie., what happens when you exercise regularly week after week). The following information is from the excellent text: Action Plan For Diabetes, by Darryl E. Barnes, MD.
Acute effects of exercise
During exercise, muscles use glycogen (the storage form of glucose in muscle) for energy. When glycogen is depleted, the muscle restores this loss by taking glucose out of the blood. Insulin plays a key role in controlling glucose transport into cells.
During exercise, cells become more sensitive to insulin. This allows glucose to be transported into the cells at a faster rate and, in turn, reduces the blood glucose level.
But, in type-1 diabetes, there isn't enough insulin. In type-2, insulin is available, however, its effect is diminished (ie., "insulin resistance").
Fortunately, during exercise, muscle cells take up glucose even if insulin is not present. Thus, exercise is highly beneficial for diabetics in 2 ways:
- exercise increases insulin sensitivity
- exercise increases glucose uptake (into muscle cells) independently of insulin
Both of these processes help to lower the blood glucose level. The process is the same for diabetics and non-diabetics. In fact, the effects of exercise can be so effective that in some non-diabetics, aerobic exercise can even reduce blood glucose levels below the normal range (70-100 mg%) (Felig P, et al. 1982).
Nevertheless, the effects of aerobic exercise on glucose/glycogen metabolism are very therapeutic in diabetics.
Chronic effects of exercise
The chronic effects of exercise are related to the increase in metabolically active muscle. Regular exercise over time produces more active muscles, which in turn use more glucose, keeping the blood level in control. These improvements in glucose metabolism can be seen within one week of starting aerobic activities. However, if you stop exercising, these effects can be reversed in as few as two days.
The benefits of regular exercise in diabetes are several:
• Improvements in glycosylated hemoglobin: Glycosylated hemoglobin, or hemoglobin A1C, shows the status of glucose levels over the previous three-month period. People with type-1 diabetes experience positive effects from exercise similar to those experienced by people with type-2 diabetes. However, in those with type-1 diabetes, the changes are entirely dependent on insulin doses and diet.
• Improved circulation: Microscopically, a muscle that has been exercised regularly has an increase in the number of very small vessels (called capillaries) compared to a muscle that has not been exercised. An increase in capillary density allows more blood flow to active muscle which, in turn, increases the efficiency of glucose metabolism.
• Weight loss: Weight loss is a common result of exercise in a person with type-2 diabetes. Typically weight loss will improve the overall health of someone with type-2 diabetes and will decrease the need for insulin in those who are dependent on it. However, a review of 14 studies on the effects of exercise in diabetics showed that exercise improves glycemic control even if no weight is lost (Boule NG, et al. 2001).
OFFICIAL EXERCISE RECOMMENDATIONS FOR DIABETICS
So, this brings us back to the original questions: What kind of exercise is recommended for diabetics? Is aerobic exercise better than resistance exercise? And how much exercise is necessary? How often? How intense?
In a thorough review, John Ivy, PhD at the University of Texas at Austin concluded that resistance exercise improves insulin sensitivity to about the same extent as aerobic exercise (Ivy JL. 1997). Hemoglobin A1C is lower in diabetics who exercise regularly. It didn't make any difference whether exercise was aerobic exercise or resistance exercise (Boule NG, et al. 2001). However, for reasons discussed below, aerobic exercise is generally preferable than resistance exercise for diabetics.
Official exercise recommendations for diabetics come from the American Diabetes Association (ADA), and from the American College of Sports Medicine (ACSM). In 2000, the ACSM published a position statement recommending exercise for people with diabetes. This was followed in 2002 by similar recommendations from the ADA (note that the recommendations pertain specifically to type-2 diabetes):
All adults with type 2 diabetes should obtain at least 150 minutes
of exercise or physical activity each week.
This works out to roughly 30 minutes per day, 5 days per week.
AEROBIC EXERCISE AND DIABETES
The official guidelines listed above state how long to exercise, but not how hard, or what kinds of exercise are best.
In terms of mortality, a study from the CDC concluded that 2 hours of walking per week lowered the mortality rate in adults with diabetes by 39%. Mortality rates were even lower for those who walked 3-4 hours per week. The researchers calculated that one death per year could be prevented for every 61 people who walk at least 2 hrs/week (Gregg EW, et al. 2003).
Since then, official exercise recommendations have been refined somewhat. How LONG to exercise depends on how HARD you exercise:
|• How long?
||jogging, running, tennis...
RESISTANCE EXERCISE AND DIABETES
Research shows that 6 months of resistance exercise improves insulin action in older adults, both males and females (Ryan AS, et al. 2001). However, there are some additional issues to consider when diabetics engage in resistance exercise:Weight-lifting (by anyone) can momentarily drive blood pressure up to astronomical levels. In one report, the brachial artery pressure in a weight-lifter during leg press hit 480/350 mmHg (MacDougall JP, et al. 1985).
One of the complications of diabetes is a change in blood vessels. A concern in diabetics is that such high pressures may damage the tiny vessels of the retina. Peter A. Farrell, PhD, Department of Exercise Science at East Carolina University, writing in a Gatorade Sports Science Institute publication in 2003 states: "Until resistance exercise is proven harmless, the person with diabetes who has preexisting retinal damage should avoid this type of exercise."
PREVENTING DIABETES WITH EXERCISE
So, it's clear that exercise is good for people with diabetes. The obvious next question becomes: Can the risk of developing diabetes be reduced by exercising regularly? And, the answer is, "yes" though genetics may influence this (Laaksonen DE, et al. 2007).
Research from two randomized trials shows that 150 minutes of physical activity per week, combined with weight-loss of 5-7%, reduced the rate of progression from pre-diabetes (aka: impaired glucose tolerance) to diabetes by 58% (Sigal RJ, et al. 2006). And results from the Finnish Diabetes Prevention Study also showed a dramatic decrease in the risk of developing type-2 diabetes in adults with existing glucose intolerance. In this study, changes in lifestyle included not only more physical activity, but, also, weight loss, and dietary changes (Lindstrom J, et al. 2006).
A study from the Harvard School of Public Health, published in 1999, analyzed whether walking pace made any difference in the risk of developing diabetes. This study was conducted in over 70,000 female nurses, ages 40-65, who did not have diabetes. The researchers found that faster walking was better than moderate walking, and, moderate walking was better than slow walking (Hu FB, et al. 1999).
And, there's also evidence that participation in college sports reduces the risk later in life (Frisch RE, et al. 1986). Several explanations could account for this, but it certainly argues for the long-term health benefits of sports and exercise.
SPECIAL GUIDELINES FOR DIABETICS WHO EXERCISE
First, as with any person who is over 40, obtain clearance from your physician before starting a new exercise program, especially if you are out of shape. This may include a stress test. Baseline hemoglobin A1c level should be measured.
The best time of day for diabetics to exercise is in the morning; disturbances in blood glucose are less likely if exercise occurs before breakfast and before the morning dose of insulin (Farrell PA. 2003). Since blood glucose levels can change rapidly, check blood glucose both before and after exercising.
Peter Farrell, PhD, offers these guidelines:
- If blood glucose is < 5 mM (90 mg/dl), some carbohydrates before exercising will likely be needed.
- If blood glucose is 5-15 mM (90-270 mg/dl), extra carbohydrate may not be required.
- If blood glucose is > 15 mM (270 mg/dl), delay exercise and measure urine ketones. If urine ketones are negative, exercise can be performed; no additional carbohydrates are necessary. If urine ketones are positive, administer insulin, and delay exercise until ketones become negative.
Regarding aerobic exercise, monitor RPE (ratings of perceived exertion) instead of exercise heart rate. Diabetes affects nerve conduction and this, in turn, may affect the relationship between exercise intensity and exercise HR.
Sports like football and track and field, because activity is intermittent over a prolonged period of time, make it more difficult to balance food intake and insulin doses. Stop exercising immediately if you begin to feel nauseated or confused.
An important recommendation for diabetics is to wear thick socks and good shoes when exercising. Diabetics may not perceive when a blister is forming and this could predispose them to infections.
If you, or your athlete, is a diabetic with documented ophthalmic complications of diabetes, resistance exercises and any heavy-lifting activities should be discouraged.
Q: You've said that regular exercise is important for the health of diabetics. But, can I still be competitive at an elite level if I have diabetes?
ANSWER: The short answer to this is, yes, you definitely can. Even with diabetes, athletes can succeed at an elite level:
- Pro Football: Jay Cutler is currently the quarterback of the Chicago Bears. He has type-1 diabetes.
- Sprint swimming: Gary Hall Jr. (USA) won a gold medal at the 2004 Athens Olympics in the 50-meter freestyle.
- Rowing: Sir Steven Redgrave (UK) won several gold medals in rowing at 5 successive Olympic Games from 1984 to 2000.
Nevertheless, as mentioned previously, diabetics need to be aware of several issues:
- Neuropathies: Neuropathies are a complication of diabetes. This may affect the heart rate response to exercise, thus making it more difficult to monitor exercise intensity.
- Retinopathies: If there is any evidence of retinal damage, weight-lifting (because of blood pressure increases) and sports/activities such as boxing, football, hockey, karate, and judo (because of contact to the head and face) should be avoided.
As summarized above, we are facing a global health crisis from the combination of obesity and diabetes. A sedentary lifestyle is a contributing factor in both conditions. While exercise is important for everyone, it is especially important for those who are:obese, have diabetes or pre-diabetes or have a family history of diabetes. Studies show that regular exercise is not only helpful in managing diabetes, but it may also reduce the chances of developing diabetes in these high-risk groups.
So, if you have diabetes, can you exercise? Yes, you can, and, more importantly, you should!
FOR MORE INFORMATION
An excellent resource for diabetics who want information on exercise is Action Plan for Diabetes, by Darryl E. Barnes, MD.
Weekend warriors and more serious athletes with diabetes may want to read: Diabetic Athlete's Handbook by Sheri Colberg, PhD.
The American Association of Clinical Endrocrinologists maintains the web site Empower Your Health (www.EmpowerYourHealth.org) that offers consumer information on diabetes.
The National Diabetes Education Program (NDEP) offers a variety of educational documents on their web site at: www.NDEP.NIH.gov.
The CDC offers a variety of consumer resources on diabetes, including the National Diabetes Fact Sheet that can be downloaded in PDF format. This CDC web site is called the Diabetes Public Health Resource and can be accessed at www.CDC.gov.
For athletes with diabetes: The Diabetes Exercise and Sports Association (DESA) was founded in 1985 by Paula Harper under the name "International Diabetic Athletes Association (IDAA)", but the name was changed in 2000. In 2011, DESA merged with Insulin Independence, a non-profit organization that was founded in 2005. It appears that DESA has now been retired. Information on Insulin Independence can be found at: www.insulindependence.org
Other useful web sites include:
For health care professionals: Both the American College of Sports Medicine (ACSM) and the American Diabetes Association (ADA) published position statements recommending exercise for people with diabetes. In addition, an outstanding summary of research on exercise and diabetes is the paper by Sigal, et al. 2006 (see "References" below). The Gatorade Sports Science Institute document, written by Peter Farrell, PhD (listed below in References) is an excellent resource for health care professionals.
Readers may also be interested in:
EXPERT FITNESS ADVICE
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ABOUT THE AUTHOR
Stan Reents, PharmD, is a former healthcare professional. He is a member of the American College of Sports Medicine (ACSM) and holds current certifications from ACSM (Health & Fitness Specialist), ACE (Personal Trainer, Health Coach) and has been certified as a tennis coach by USTA. He is the author of Sport and Exercise Pharmacology (published by Human Kinetics) and has written for Runner's World magazine, Training and Conditioning, Club Solutions, and other fitness publications.
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