We are starting to get into the winter months; many of us will certainly be slowing down on our activity levels.

In some cases this will be a good thing since a large number of athletes and very active people overdo their efforts and do not allow their bodies time to heal up and rest during the active months of summer. Those of us who are very active usually do not get enough caloric intake, which can also slow the recovery and healing process.

One of the more common health issues that come from being extremely active is fatigue. Over-training or extreme activity with little downtime, along with an inadequate diet and sleep, can zap your energy levels.

Here is a great starting point if you're active and feel like you struggle with bouts of chronic fatigue. Poor diet or low caloric intake based on your energy output is a great place to look. Then consider that in seasons of extended daylight hours we tend to sleep less; this reduction in your sleep hours can catch up with you over time. Also consider that most of us live with busy schedules so stress can add to the mix and recent studies have shown that anemia is more common with endurance athletes and runners than other active people.

It is important to maintaining an active lifestyle, so modifying your exercise regimen and increasing your healthy food intake is a very good way to start managing exercise-related fatigue.

Here are a few other common reasons you may be feeling fatigued, and ways you can start to correct and counter these challenges.

* Too Little Rest and Recovery: The most common cause of fatigue in active people and athletes at every level is inadequate rest and recovery. When we combine the demands of training and exercise with the responsibilities of work and family, the hours available for rest and recovery quickly become nonexistent.

The body makes physiologic gains during rest. Everyone needs adequate nightly sleep. Research has shown 7-10 hours of sleep is best. However, naps and meditation can also be used to supplement your nightly sleep. Individuals vary in the amount of rest needed but there is no question that as training and life demands increase, attention to rest and recovery must also increase.

* Don't Limit Your Calories: Inadequate caloric intake is another common cause of fatigue. Dieters, active busy people and athletes frequently lack or limit calories some with the goal of weight loss. Others unintentionally eat too little calories for their training or activity load.

Finding a balance between adequate caloric intake and good nutrition is no easy task. Building a solid nutrition program and using a calorie calculator is one approach that works well. You can find a number of good calorie calculators for your smart phones or on the intranet. Following your caloric intake over a course of a few months is the best way to manage this common cause of fatigue.

* Low Iron Level: Low iron can also cause fatigue. Iron is the key building block of hemoglobin, the oxygen-carrying molecule of red blood cells. When your body lacks sufficient iron, it cannot optimally deliver oxygen to working muscles. Sources of iron include red meats, spinach and kidney beans.

The diagnosis of iron deficiency requires evaluation and blood testing by your doctor. Be cautious when taking iron supplements without medical supervision. Too much iron in your system can cause a number of serious health issues.

* Thyroid Dysfunction: Although thyroid dysfunction is not common, it can be a source of fatigue. Evaluation and testing by your doctor can generally differentiate between various causes of thyroid dysfunction.

Hypothalamic-adrenal dysfunction is most typically seen in people and athletes of all levels who over-train or severely lack rest and proper recovery from extended activity. Most frequently seen are lower than normal levels of testosterone, estrogen, growth hormone, cortisol and luteinizing hormone and follicle stimulating hormone.

* Colds and the Flu: Getting sick can really impact a person's ability to fully recover to normal energy levels. Viral illnesses such as colds, the flu and bronchitis adversely affect everyone to varying degrees. Most people view these illnesses as short-term setbacks to their health and fitness, but then find that it can take months to get their energy levels back to normal.

* Seasonal affective disorder: It is estimated that about 6 percent of the U.S. population gets seasonal depression, often called seasonal affective disorder. SAD is a depression that occurs each year around the same time, usually starting in fall or winter. Many people start feeling fatigue, crave more sleep, wake with less energy and find it difficult to concentrate.

The best way to combat this is spending time outdoors, keeping active with exercise plus good nutrition, and in some cases light therapy has proven effective.

* Cardiac Disease: This should never be overlooked when evaluating fatigue in active people. Many times the initial symptoms of cardiac disease is very non-specific such as mild fatigue, out of breath very easily, and or feeling dizzy. You should always make your doctor aware of these symptoms. Your doctor can perform a few simple tests thatcan generally tell if you need more extensive testing of you cardiovascular system.

Fatigue can tell us many things. It lets us know we are applying an appropriate level of training. It tells us if we need to take a break for rest and recovery. It can also just be the start of the winter blues due to lack of fresh air and sunshine.

However, atypical symptoms of fatigue or feelings of fatigue that do not resolve with rest, recovery and better nutrition can be signs of more serious health concerns. Pay attention to your body, evaluate your eating and sleep habits and seek out your doctor to ensure your health is not at risk.

Judd Jones is a director for the Hagadone Corporation.