~Dr. Gabe Mirkin's Fitness and Health e-Zine
A new study suggests that it is the level of fitness, not time spent sitting, that predicts susceptibility to disease and longevity (Mayo Clinic Proceedings, published online October 18, 2016). Heart-lung fitness is the ability of the heart and lungs to provide oxygenated blood to contracting muscles for prolonged periods. In this study from Norway, the authors followed 495 women and 379 men, aged 70 to 77 years. They measured sitting time with accelerometers and heart-lung fitness by peak oxygen uptake (VO2 peak). They found that:
* People who spent 12-13 hours sitting each day were 75 percent more likely to have heart attack risk factors (high blood pressure, obesity, diabetes, high cholesterol, high waist circumference, high triglycerides, reduced good HDL cholesterol, high blood pressure, and high fasting blood sugar levels).
* The most fit people were more than 40 percent less like to have abnormal heart attack risk factors, even if they sat for 12 to 13 hours a day and did not meet the criteria for the recommended amount of exercise done each day.
* People who exercised, but were not physically fit, were not protected from the heart attack risk factors.
Another new study from Rotterdam shows that exercisers live significantly longer than non-exercisers and suffer far fewer heart attacks. For the average Rotterdam citizen, cycling provided the highest level of fitness and was associated with a man living 3.7 years longer than his non-cycling countrymen (Journal of Public Health, 10/31/2016).
Sitting Will Not Harm Vigorous Exercisers Asking people to stand at work, rather than sit, is not good advice because standing-without-moving is no better than sitting, and will make you too tired to exercise vigorously when you are finished working. If you are a vigorous exerciser, standing all day will slow your recovery from your exercise program.
The highly-publicized studies that showed sitting is harmful for exercisers were flawed because they failed to separate casual exercisers from vigorous exercisers. No one has shown that standing up instead of sitting confers any special health benefits, and standing without moving around can cause additional problems such as varicose veins and swollen feet. Contracting muscles circulate extra blood to strengthen your heart and draw sugar from the bloodstream to lower high blood sugar levels. This does not happen when you just stand in one position without moving your muscles.
The White House requested $700,000 worth of standing desks for its employees. I think this is foolish and a waste of money. Instead of pushing people toward minimal exercise during work, they should encourage people to exercise more intensely, either in properly-equipped exercise facilities at the workplace or during their leisure time.
Exercise desks with treadmills or pedals should be recommended only for people who are unable to exercise properly. Moving while you are trying to concentrate on work, reading or anything else gives you minimal muscle movement and does not make muscles stronger or increase endurance. To make muscles stronger, you have to damage them with vigorous exercise and when they recover, they become larger and stronger. You cannot increase your ability to take in and use oxygen unless you exercise vigorously enough to become short of breath, and this will never happen at a treadmill desk.
Sitting is Harmful for Non-Exercisers at Any Age Older people who move around live longer than those who are consistently sedentary, and sedentary older people who become more active live longer than those who remain sedentary (Med & Sci in Spts & Ex, Aug 2013;45(8):1501-1507). In this study, the more time people sat, the more likely they were to:
* have a big belly (a sign of high blood sugar levels)
* have high blood pressure
* have high HBA1C blood test (a measure of high blood sugar)
* have a high CRP blood test (a measure of inflammation)
* have higher blood sugar levels
* have heart disease
* have diabetes
* be a smoker
* be overweight
Problems with Studies on Harm from Sitting Most studies that appear to show that prolonged sitting time is harmful have focused only on single indicators such as self-reported sitting, TV viewing, screen time or traveling in a car (Br J Sports Med, 2015;49:737–42). A recent study corrected for this by analyzing total exercise time. Dr. Richard Pulsford of the University of Exeter in the UK followed 3,720 healthy men and 1,412 healthy women for 16 years and found that total time sitting, time sitting at work, watching TV and during leisure time with or without TV were not associated with increased risk of death during the study period (International Journal of Epidemiology, October 9, 2015). The authors corrected their data for age, gender, socioeconomic status, smoking status, alcohol consumption, diet and general health. They showed that prolonged sitting time is not damaging to health if you exercise regularly.
The earlier report that made headlines, from The University of Toronto, reviewed 47 studies and found that sitting for more than eight hours a day was associated with increased risk for death from heart attacks, diabetes, and cancers of the breast, colon, uterus, and ovary, even if a person exercises (Annals of Internal Medicine, 2015;162(2):123-132). The authors believe that people are harmed by spending more than four to five hours a day sitting, driving a car, using the computer or watching television. One study cited in the review showed that people who sat less than eight hours a day had a 14 percent lower risk of being hospitalized. Other studies also associate prolonged time spent sitting with increased risk for weight gain, disease and premature death (Br J Sports Med, Jan 2015;49(2):95-9; J Am Coll Cardiol, 2013 Jun 11;61(23):2346-54). However, virtually none of the people in these studies were doing enough intense exercise to be at a high level of fitness, let alone to be able to compete in sports. The authors define high levels of physical activity as "at least 20 minutes a day of vigorous exercise or at least seven hours a week of moderately vigorous exercise." This meager amount of exercise is far less than serious exercisers would usually do.
Other recent studies have shown that prolonged sitting is associated with increased risk for fatty liver disease (Journal of Hepatology, November 2015;63(5):1229–1237), and greater risk for total cancers in women, but not in men (Cancer Epidemiology, Biomarkers, and Prevention, July, 2015). Neither of these studies separated vigorous exercisers from casual exercisers or non-exercisers.
Why Casual Exercise May Be Less Beneficial than Vigorous Exercise A high rise in blood sugar causes sugar to stick to the outside surface of cells throughout your body and causes significant damage (American J. of Clinical Nutrition, April 2010; Archives of Internal Medicine, May 2010). Resting muscles pull virtually no sugar from your bloodstream, and insulin is required for the little amounts of sugar the muscles use. Contracting muscles can draw large amounts of sugar from the bloodstream and don’t even need insulin to do so. The more vigorously you exercise,
* the more effectively your muscles remove sugar from the bloodstream without needing insulin, and
* the longer your muscles continue to draw sugar from your bloodstream without needing insulin after you finish exercising (Am J Clin Nutr, 2008(July);88(1):51-57).
After a vigorous exercise session, your muscles can continue drawing sugar without needing insulin for up to 17 hours (J Appl Physiol, 2005;99: 338-343 & 2005;8750-7587). Preventing high rises in blood sugar helps to prevent diabetes, heart attacks, strokes, impotence, dementia and premature death. Vigorous exercise is also the key to increasing the numbers and size of mitochondria, which helps to prevent overweight, diabetes, heart attacks and certain cancers.
Vigorous Exercisers Need to Sit or Lie Down People who exercise intensely need to spend a lot of time sitting or lying down because muscles are damaged by intense exercise. All successful athletes train by stressing and recovering. They take a workout that is intense enough to damage their muscles, and then they take easier workouts to allow their muscles to recover for their next hard work out. Without the muscle damage caused by intense exercise, muscles do not grow and become stronger. If exercisers don’t spend enough time resting their muscles after an intense workout, their muscles will take longer to heal, which will delay recovery. It will take longer for them to be able to take their next workout, or worse, they may suffer an injury.
* Everyone should move their muscles to keep fit.
* A high level of fitness is a far better predictor of longevity and freedom from disease than measures of time spent sitting or standing.
* If your job requires prolonged sitting or sedentary standing, balance the effects of this inactivity with a program of vigorous exercise to keep yourself fit.