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New Study Finds Too Much Exercise Can Delay Pregnancy in Normal-Weight Women

April 06, 2012 | 29,916 views
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By Dr. Mercola

Even though exercise is extremely healthy -- it's the closest physical strategy to a "miracle drug" that I can think of -- it's becoming increasingly clear that too much exercise is not.

For most people this is not an issue, because most people are not exercising enough -- and particularly not intensely enough.

But there are instances where you need to carefully consider your exercise strategy to make sure it is in line with, and supporting, your health goals.

Optimizing your fertility and how long you will live are examples.

If You're Normal Weight and Want to Get Pregnant, Avoid Over-Exercising

New research in Fertility and Sterility looked into the association between physical activity and time to pregnancy.

Among women who were overweight or obese, any type of exercise improved fertility.

But among normal-weight women, higher levels of vigorous exercise -- such as running on a treadmill for an hour five days a week -- appeared to make it harder to conceive, as it led to delays in becoming pregnant.

It's long been known that strenuous exercise can cause disturbances to a woman's monthly cycle, leading to a lack of ovulation and menses, along with other fertility problems.

This is particularly common among competitive female athletes and marathon runners.

However, the study's author, Lauren Wise, an associate professor of epidemiology at the Boston University School of Public Health, suggested high-intensity exercise might also disturb implantation (when a fertilized egg attaches to the uterus).

Moderate exercise, on the other hand, led to faster times to pregnancy among all women. Only very vigorous exercise -- which was defined as running, fast cycling, gymnastics or swimming for more than five hours a week -- appeared to delay exercise in normal-weight (but not overweight or obese) women. Researchers concluded:

"These findings indicate that PA [physical activity] of any type might improve fertility among overweight and obese women, a subgroup at higher risk of infertility. Lean women who substitute vigorous PA with moderate PA may also improve their fertility."

Why Less is Sometimes More When it Comes to Exercise

A growing body of research shows you may not need to spend as much time exercising as you think -- provided that you are willing to put in some authentically vigorous effort when you do. Incorporating high-intensity interval training such as that advocated by fitness experts Phil Campbell or Dr. Doug McGuff can improve your fitness regimen. These types of exercises dramatically cut down on your exercise time while producing greater benefits—simply because you're using your body as it was designed to be used.

When doing high-intensity anaerobic exercises like Peak Fitness, you can literally be done in about 20 minutes, compared to spending an hour running on the treadmill. And according to Dr. McGuff, if you're doing Super Slow strength training, which is another form of high-intensity type training, all you need is 12 minutes a week. Yes, you read that right: 12 minutes a week!

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If you perform Peak Fitness exercises correctly, it will trigger the release of human growth hormone (HGH), also known as "the fitness hormone," which accounts for many of the health benefits of interval training.

But be mindful of your current fitness level and don't overdo it when you first start out. Also keep in mind that there's no "magical" speed here. It's entirely individual, based on your current level of fitness. Some may reach their anabolic threshold by walking at a quick pace, while others may need to perform a mad-dash to get the same effect.

The remarkable effectiveness of interval training makes logical sense when you consider that this type of exertion mimics how our ancestors lived. This is also how animals and young children behave naturally (long-duration exercise really isn't "natural"). By exercising in short bursts, followed by periods of recovery, you recreate exactly what your body needs for optimum health. That said, engaging in these high-intensity exercises two to three times a week is likely to lead to a decrease in body fat.

If you are seeking to get pregnant, or compete athletically, you will need slightly higher body fat stores to be in the optimal range. This may be one reason why lean women engaging in too much vigorous exercise took longer to become pregnant. The study defined about five hours a week as too much, so it's likely that Peak Fitness exercises, which take only 20 minutes for the entire workout (with only four minutes of intense exercise) and should only be performed two or three times a week, max, would actually be beneficial.

What to Eat After Exercise to Help Optimize Fertility

Interestingly, it is virtually impossible to simultaneously optimize for both longevity and competitive fitness in terms of what you eat after a workout. This is because consuming fructose after you exercise will increase production of the hormone somatostatin, a primary purpose of which is to inhibit the production of HGH.

For most people, increasing HGH through high-intensity interval exercise is an important factor for optimizing health and longevity, so most of my readers will want to avoid sugar, fructose and juice following their workouts. But if you are seeking to optimize your fertility, or compete athletically, consuming some carbs, preferably dextrose-based, in the recovery period is probably a good idea to improve your recovery time and maximize your fertility or athletic performance. If you are not concerned about fertility or athletic performance, then lower carbs and lower percentage of body fat would be a more appropriate goal.

More Strategies for Optimizing Fertility

An estimated 1 in 6 American couples struggle with fertility each year, and there's compelling evidence that lifestyle, diet and environmental exposures are largely to blame. Not only are you exposed to hundreds (if not thousands) of toxins each and every day, but some of the most commonly prescribed drugs, poor diet, and common vitamin deficiencies have also been linked to reduced fertility, just to name a few.

As Iva Keene, author of the Natural Fertility Prescription, stated:

"Conventional IVF and other assisted reproductive technology (ART) treatments don't address root causes of infertility. These root causes can include: nutritional deficiencies, toxin exposure, stress, food intolerances, allergies and immune deficiencies. These subtle but critical factors interact synergistically to impact the quality of your eggs and sperm, affecting your ability to conceive and the health of your embryo.

… during the generation and maturation of gamete cells -- sperm and ovum -- that form an embryo [a period of 120 days], everything that you and your partner ingest, inhale or are exposed to will influence the health of your eggs and sperm for better or worse, and the ultimate quality of the genetic building blocks you pass onto your child. This is why it's crucial to follow a good preconception plan for a minimum of 4 months before conception. A baby is a 50-50 product of his or her parents -- therefore optimizing the quality of eggs and sperm is of paramount importance."

Some natural options to consider include:

  • Optimize your vitamin D levels with safe sun exposure, a safe tanning bed or a vitamin D3 supplement. Vitamin D impacts fertility on multiple levels, including boosting levels of progesterone and estrogen in women, which may help regulate menstrual cycles and improve your likelihood of conceiving naturally. In men, vitamin D is essential for the healthy development of the nucleus of the sperm cell, improves semen quality and sperm count, and is capable of supporting healthy testosterone levels.
  • Avoid genetically engineered food, especially corn and soy. These contain significant concentrations of the herbicide glyphosate (the active ingredient in Roundup), which has been linked to infertility in a number of studies.
  • Avoid chemicals as much as possible. Bisphenol-A (BPA), phthalates, fluoride (in drinking water), MSG, and many, many others have shown negative impacts on your reproductive health.
  • Consume a healthy diet, rich in healthy fats and antioxidants, and low in sugar and grains. Rather than eating conventional or farm-raised fish, which are often heavily contaminated with endocrine disruptors, PCBs and mercury, supplement with a high-quality purified fish or krill oil, or eat fish that is wild-caught and lab tested for purity. Eat mostly raw, fresh foods, steering clear of processed, prepackaged foods of all kinds. This way you automatically avoid hidden fructose and artificial food additives, including dangerous artificial sweeteners, food coloring and MSG. As much as possible, purchase and consume organic, locally grown and free-range foods to reduce your exposure to pesticides, fertilizers and other toxins.
  • Identify potential gluten intolerance. Celiac disease (gluten intolerance) has been linked to fertility problems in both sexes. In men, it's associated with abnormal sperm, such as lower sperm numbers, altered shape, and reduced function. Men with untreated celiac disease may also have lower testosterone levels.
  • Be aware of electromagnetic fields (EMFs), as research suggests cell phones may impact sperm quality as well. One study found men who talked on a cell phone for more than four hours a day had the lowest average sperm counts (50 million per milliliter) and the least healthy sperm.i


  • i Study presented at the 2006 American Society for Reproductive Medicine conference in New Orleans
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