Research Blog

Exercise into Influenza

electron microscope of flu virus

Too frequent exercise may increase risk of contracting the flu during an epidemic.  

Like many unfortunate people this winter I had to suffer through the flu. For me, it was easy to see a link between excessive exercise and catching the flu. I developed flu-like symptoms the very night after completing a long run and bike ride. I awoke the next morning to an unwanted flu. There has been a lot of research done on the flu’s link to exercise.

In 2008, a study entitled Is Exercise Protective Against Influenza-Associated Mortality looked at the association between physical exercise frequency and influenza-associated mortality risk of Hong Kong residents. The study found that those who exercised moderately (once per month to three times a week) showed the smallest risk of influenza mortality. People who reported exercising frequently (4 or more times per a week) showed no significantly lower risk of influenza mortality than those who reported never/seldom exercise (less than once a month). The results were statistically the same even when controlling for environmental and lifestyle factors. 

The researchers explain these results through exercise’s affect on immune function and recovery. Exercise results in beneficial effects on immune function through viral clearance function, antibody titer and neuroendocrine factors. However, exercise also results in impaired immunity requiring a recovery period.

To convolute the exercise and infectious disease relationship further, a study published in 2000 found an inverse relationship between physical activity and upper respiratory tract infections in healthy, elderly people. The study, entitled The symptomology of upper respiratory tract infections and exercise in elderly people, looked as the number of days and number of independent episodes of upper respiratory tract infections in subjects from ages 66-84.

Apparently, if not contracting influenza is your number one priority this winter avoid excessive exercise. However, as the authors of the 2008 study recommend, exercise should only be limited when an influenza outbreak is present.  

Please comment on this research and your personal experiences with exercise and the flu.

Take the whole fruit!


Studies show that nutritional value is lost when raw fruit is processed.

Is drinking 100% Juice as nutritionally beneficial as eating the raw fruit? Several studies have been conducted to answer this question. In 2005 a German study entitled Processing Strawberries to Different Products Alters Contents of Vitamin C, Total Phenolics, Total Anthocyanins, and Antioxidant Capacity was published to answer this question. This study, like similar studies, found that nutritional content was lost as the raw fruit (in this study strawberries) was processed. 

The researchers began by determining the amount the amount of vitamin C, phenolics and anthocyanins in raw strawberries. Raw strawberries were then processed into juice, nectar, wine and puree using various procedures. After each procedure the nutritional content retained was determined. The researchers found that pasteurization and fermentation resulted in significant reductions in nutritional value. Pasteurized juice was determined to retain just 36.0% and 35.6% of the raw strawberries' vitamin C and phenolics, respectively. Conversely, press-made juice was shown to retain 75.5% vitamin C and 61.0% phenolics. The procedures used to get to the end product showed large disparities in their respective reductions in nutritional content. Consider wine (strawberry wine anyone?), which can be produced from mash or from juice.  Vitamin C content relative to the original raw strawberries was around 35% regardless of whether or not it came from mash or juice. However, phenolics relative to the raw strawberry was 62.6% in wine made from strawberry mash and only 46.9% in wine made from strawberry juice.

These results have beed confirmed in two separate studies appearing in the Journal of Agriculture and Food Chemistry, both in 2008. Their titles are Influence of Processing on Quality Parameters of Strawberries and Processing and Storage Effects on Monomeric Anthocyans, Percent Polymeric Color, and Antioxidant Capacity of Processed Blackberry Products.

In conclusion, take the whole fruit!

Melanoma and it's Link to Height, Weight, Exercise


Photo: Melanoma on the skin.  Melanoma has been shown to correlate with height, weight an exercise.

Photo Credit:                      Terence O’Grady, M.D.                  School of Medicine                  UCSD 

A study in 2001 entitled Melanoma Risk in Relation to Height, Weight, and Exercise (United States) by Andrew Shors, Cam Solomon, Anne McTiernan and Emily White found that there is a positive correlation between height, weight and weekly exercise and melanoma risk. The authors speculated that an increased weight and height increases the amount of skin cells on the body surface that can possibly become cancerous. Weight explained some, but not all, of the correlation between risk of developing melanoma and weekly exercise. 

Although not very prevalent, melanoma is the most dangerous skin cancer.  It occurs when melanocytes, cells that produce skin-darkening melanin, become malignant. Unless detected early, it is almost always incurable. Unfortunately, melanoma rates have been increasing in the general population. For these reasons, understanding, preventing and curing melanoma is a top medical priority.   

In the aforementioned study, melanoma risk was found to correlate with commonly known risk factors: age, light hair color and skin color, freckles, and tanning ability. This was the first study to provide a correlation between exercise and melanoma risk. The authors theorized that exercise may reduce melanoma risk through two pathways: reducing BMI as mentioned above and by metabolic effects like strengthening the immune system and influencing various hormones' production.

Feeling Tired This Winter?

During the winter months light pollution’s affect on melatonin production is especially damaging to human health.

Many studies have shown that melatonin levels fluctuate seasonally. Melatonin is a hormone that is produced with the circadian rhythm by the pineal gland.  Interestingly, melatonin production is inhibited by blue light. Melatonin directly causes drowsiness, thermoregulation (your body temperature drops during sleep), changes in blood pressure, and glucose homeostasis.  In addition, melatonin secretion is used to regulate seasonal biological functions such as reproduction. The body accomplishes this by using a changing day-to-night ratio that occurs as the seasons change.

In 1991, a study by Dr. Thomas A. Wehr entitled The Durations of Human Melatonin Secretion and Sleep Respond to Changes in Daylength (Photoperiod) showed through artificial photoperiods that melatonin production could be changed. Dr. Wehr questioned whether such changes in melatonin levels would lead to significant seasonal changes in human physiology and behavior.  In 2010, Harvard School of Medicine and the Brigham and Women’s Hospital published a study with 116 subjects showing that even bedroom light or dim light inhibited melatonin production before bedtime. About 90 minutes of melatonin production was lost on a daily basis by electrical lighting. The authors cautioned against chronic exposure to electrical light and its effect on daily biological functions.  

In October of 2011, Italian scientists published a study showing that the migration from sodium lamps to metallic halide lighting and LEDs would result in a five-fold increase in light pollutions's effect on melatonin production. The authors warned that unless lighting had stricter regulations, light pollution's known and unknown consequences to human health and the environment would increase.

During the winter months light pollution is especially acute because much of the evening is spent under artificial light.

Some Background Information on Exercise Research Terms

From a 1985 article in the Public Health Reports:

Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research.

Authors: C J Caspersen, K E Powell, and G M Christenson

"Physical activity," "exercise," and "physical fitness" are terms that describe different concepts. However, they are often confused with one another and the terms are sometimes incorrectly used interchangeably. This paper proposes definitions to distinguish them. Physical activity is defined as any bodily movement produced by skeletal muscles that results in energy expenditure. The energy expenditure can be measured in kilocalories. Physical activity in daily life can be categorized into occupational, sports, conditioning, household, or other activities. Exercise is a subset of physical activity that is planned, structured, and repetitive and has as a final or an intermediate objective the improvement or maintenance of physical fitness. Physical fitness is a set of attributes that are either health- or skill-related. The degree to which people have these attributes can be measured with specific tests. These definitions are offered as an interpretational framework for comparing studies that relate physical activity, exercise, and physical fitness to health.

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