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Wednesday, September 22, 2010

You May Not Be Getting Enough of These Nutrients

An article in the September 2010 issue of the Nutrition Action Health Letter contains a cover story entitled, “Getting Enough? What you don‘t eat can hurt you.” The article states that many of us are not getting enough potassium, magnesium, Vitamin D, or Vitamin B-12, with possible negative health consequences.

  • A third of Americans have high blood pressure, which increases the risk of heart attack and stroke. Over age 65, two-thirds of us have high blood pressure. More than half of those afflicted don’t have it under control.
  • Potassium can help regulate blood pressure. Major studies have shown that people with higher potassium intake have lower blood pressure.
  • A low potassium level is a predictor of stroke. A study of 43,000 subjects showed that those consuming the most potassium had 38 percent fewer strokes that those who consumed the least. The beneficial effect of potassium is the greatest for those who consume the most sodium. It is thought to work by increasing the flexibility of arteries and widening the tiny blood vessels.
  • While blood pressure typically rises as one gets older, 4 weeks on a low sodium, high potassium diet can totally reverse the effect of age on blood pressure. The DASH Diet (Dietary Approaches to Stop Hypertension), which minimizes added salt and includes 11 daily servings of fruit and vegetables as well as 2 servings of low-fat dairy products and low quantities of saturated fats, refined sugar, and refined grains, provides plentiful potassium while keep sodium down to recommended levels.
  • Potassium citrate is the form of potassium found in fruits and vegetables and it is considered more effective for blood-pressure reduction and safer than potassium supplements (usually potassium chloride), which can cause heart problems if taken in excess. Potassium citrate also reduces the risk of kidney stones by 50% and may help prevent bone loss.
 Vitamin D

  • This nutrient seems more important than calcium for protecting bones and preventing osteoporosis, a  bone-thinning disease that causes bone fractures in 25% of men and 50% of women over age 50.
  • Among Navy recruits, supplementation of 2,000 mg of calcium along with 800 IU of vitamin D per day reduced stress fractures by 20%.
  • Evidence suggests that Vitamin-D also protects against colon cancer, heart atacks, stroke, diabetes, falls, autoimmune disease, and all-cause mortality.
  • The article recommends taking a Vitamin-D supplement, as it is difficult to get the recommended amount from food. The recommended dosage is 400 IU per day for people under 60 and 800-1000 IU per day for people over 60.
  • Recommended calcium intake is 1000 mg/day for people under 50, and 1200 mg/day for people over 50.
  • Many Americans have Type II diabetes, including 25% of people over 60.
  • Diabetes greatly increases the risk of stroke, heart disease, blindness, kidney failure, nervous system damage, and limb amputations.
  • While excess body fat, lack of exercise, and poor eating habits are the major risk factors for Type II diabetes, a lack of magnesium can be a contributing factor. Large studies have shown that high magnesium intake is associated with reduced incidence of diabetes.
  • Fruits, vegetables, whole grains, nuts and beans are plentiful in magnesium. 
Vitamin B-12
  • Low levels of Vitamin B-12 are associated with poorer memory and mental ability. Yet the ability to absorb this vitamin from food decreases as we age.
  • A low Vitamin B-12 level in combination with a high levels of folic acid is strongly associated with cognitive impairment.
  • The article recommends taking a multivitamin containing at least 6 micrograms of Vitamin B-12 or a B-12 supplement containing up to 100 micrograms of B-12, and being careful not to get too much folic acid from vitamins and fortified cereals.

Monday, September 20, 2010

Static Stretching Can Impair Distance Running Performance

At times it can be difficult to find sports science articles that have true relevance to athletes. But here's one that can have real impact. A study by Wilson et al. (Journal of Strength and Conditioning Research, vol 24, no. 9, pp. 2274-2279, 2010) provides strong evidence that static stretching before a distance-running event can impair performance among young, male athletes.

Static stretching involves stretching a muscle to the point of mild discomfort and holding the stretch for 10-30 seconds. We have previously highlighted previous evidence that static stretching can impair jumping performance. It has also been shown to reduce maximal leg-press strength, 20-meter sprint speed, and knee-extension torque. Yet this is the first study to examine the effect of static stretching on endurance performance.

Experimental Procedure
10 male collegiate competitive distance-runners and triathletes who ran at least 20 miles per week and were in excellent aerobic condition were tested on 2 different days, at least a week apart, after the following:
  1. 16 minutes of stretching consisting of the following 5 stretches each performed 4 times for 30 seconds of holding:: 1) sit on floor with knees straight and reach with both hands to and beyond the toes, 2) stand with balls of feet on a block, letting bodyweight stretch calves, 3) for both left and right, stand on 1 leg and pull the opposite heel toward the butt 4) for both left and right, lunge deeply, and 5) cross the left leg over the right one, and pull the right thigh towards the torso, repeating for other side
  2. Quiet Sitting
After stretching or not stretching, the subjects underwent the following treadmill tests:
  1. Run at 65% of maximal aerobic capacity (VO2max) for 30 minutes while energy-cost is measured.
  2. After 2 minutes of rest and rehydration, run as far as possible in 30 minutes (subjects could control treadmill speed and see a time display, but not see a speed or distance display).
Experimental Results
On the no-strech day, the athletes performed significantly better as follows:
  • They covered an average of 6.0 km in 30 minutes on the no-stretch day compared to 5.8 km on the stretch day
  • They required an average of 425 calories on the stretch day vs. 405 calories on the no-stretch day to do the 30-minute submaximal run.

Bottom Line
Static stretching before running hurt the athletes' distance-running performance. After stretching they required more energy to run the same speed in the submaximal test, while in the maximal-distance 30-minute test they were not able to run as far. These differences can easily affect the chance of winning a race. The negative effect of static stretching appears to be due to a reduction in the spring-like stiffness of the leg muscles resulting in lower efficiency. Thus, it does not appear advisable to do static stretching before distance-running events. While dynamic stretching has not been subject to similar testing, it is a possible alternative. The evidence suggests that the best warmup before a distance-running event may be walking followed by jogging followed by short-distance runs at speeds increasing to race-pace.