Insomnia is a huge problem in the United States. We spend over $10 billion a year on sleep-related treatments and it's estimated we lose over $40 billion in lost worker productivity due to sleeplessness.

Insomnia is a very complex subject that I can address only briefly in this column. I'll focus on some causes of insomnia this week. It's important to remember that insomnia is not a disease - it is a symptom of an underlying problem.

There are three types of insomnia. Transient insomnia lasts a week or less and is usually due to some type of limited stress. Short-term insomnia lasts one to six months and is usually caused by persistent stress, while chronic insomnia lasts greater than six months.

There are many causes of insomnia. Transient and short-term insomnias can be caused by stress as well as environmental factors such as sleeping in an unfamiliar bed or other location. Having too much light or noise in the room can also be contributing factors.

There are numerous causes of chronic insomnia, the most common of which is probably psychiatric illness. This may include anxiety and/or depression. Trouble falling asleep is typical of people with anxiety issues. People usually report that their minds are racing and they can't turn them off. I see this frequently in patients who are multi-taskers who feel as though they never get everything finished. Depression is also a common cause of chronic insomnia, though these folks usually present with "terminal insomnia," typically waking up very early in the morning.

Pain from arthritis or other conditions like fibromyalgia can lead to chronic insomnia. Lung disease such as COPD, and heart disease, especially congestive heart failure, can lead to frequent episodes of waking at night.

Restless Leg Syndrome can cause trouble getting to sleep or staying asleep. Sleep apnea may also cause frequent nighttime wakings. Drug use is a common cause of chronic insomnia, particularly stimulants such as caffeine as well as sedatives, especially alcohol.

Caffeine is a huge problem and one of the first habits I ask about when I see someone who has trouble sleeping. People (especially teens) frequently drink too much soda, coffee or even energy drinks. I often discover they're doing it to keep themselves awake during the day because they can't sleep at night! Caffeine can stay in your system for eight hours or longer.

Over-the-counter or prescription sleeping pills can also be habit-forming. People who take these often find themselves unable to stop taking them or they require larger doses to get the same effect. These medications can also be quite dangerous in the elderly as they can cause problems with balance and coordination that can lead to falls resulting in fractures or brain injuries.

Many people subscribe to the incorrect notion that alcohol helps them sleep. While alcohol has depressant effects on the brain, it actually does not allow the brain to get into deep sleep. Deep sleep is critical for the brain to refresh itself. If the brain does not get enough deep sleep, the person constantly feels sleep-deprived.

Shift work sleep disorder is another common cause of insomnia that is typically found in manufacturing communities. This condition can result when workers either change shifts or have a brain that is wired to only function properly if they sleep at night. More and more young people are suffering from "sleep phase delay" insomnia. This results from staying up late and sleeping in late. The problem arises when they want to go to bed earlier and can't get to sleep.

Next week I'll cover prevention and treatment of sleep disorders. Pleasant dreams!