Updated June 08, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Our modern industrial society runs 24 hours a day. It seems that nothing really stops for night - and neither do we. Sometimes we find it hard to sleep well. Shift work, street lights, travel across time zones, the demands and conveniences of life in the space age - all claim to make life better, more flexible, more diverse. But can our body's natural rhythms adjust to an almost constant exposure to light, without some consequences?

You've Got Rhythm - But It May Be Irregular
Keeping your body clock on a regular schedule may play an important role in reducing your risk for breast cancer. Your circadian rhythms affect hormone levels, which in turn affect many of your body's functions, including the growth and suppression of tumors. Getting enough high-quality sleep helps protect your health and prepares you for life's daily challenges. But working the night shift, having a chronic stress load or bad bedtime habits can disrupt your body clock and weaken your immune system, lowering your natural defenses.

Working Night Shift and Increased Breast Cancer Risk
The International Agency for Research on Cancer (IARC) did a recent study, which suggests that shift workers do have significantly higher rates of cancer. But an extensive Swedish study concluded that, except for an increase in thyroid cancers in men, there is no such association. These studies may disagree because they look only at sleep patterns. But other factors influence cancer rates.

Dr. Margaret Lewin, the Medical Director of Cinergy Health explains, "For example, increased breast cancer rates could be related to the fact that night shift workers in general drink more alcohol, or that airline stewardesses (who work alternating shifts and seem to have a higher risk of breast cancer) are also exposed to higher amounts of cosmic radiation (another risk factor) than the general population." Since lifestyle and environmental factors must be considered along with sleep patterns, it has been difficult to design and carry out a study that would provide definitive answers about shift work and cancer risk.

Quality And Quantity Of Sleep
Sleep is so important that studies have been done on how much of it you need to lower your risk of breast cancer. Dr. Lewin noted that, "The answer to the question about how much sleep you need to prevent breast cancer remains controversial." A Finnish study found that women who consistently slept 6 hours or less every night had a slightly higher rate of breast cancer than those who slept 7 to 8 hours; and women who consistently slept 9 hours or more had the lowest risk. However, a study done at Brigham and Women's Hospital in Boston found that that womens' death rates in general increase in those sleeping more than 7 hours a night. The answer may be a mix of factors: time spent sleeping, and quality of sleep, which can vary with each person. Medical and psychological conditions can affect sleep quality, as can environment and lifestyle.

Melatonin - The Natural Prescription for Good Sleep
Your body produces melatonin when you are in darkness - too much light means less melatonin and less healthy sleep. Melatonin can suppress estrogen, a hormone that fuels 80% of all breast cancers. So while you're sleeping, you have less circulating estrogens, and the growth of breast cancer cells slows down. You can't buy good sleep, even though you can buy melatonin, according to Dr. Lewin. "Natural melatonin is released in cycles during sleep and is thought to be a major contributor to the beneficial aspects of sleep. These natural cycles are not reproduced by taking a pill - that produces a peak concentration in the body - which drifts down as the pill's effect wears off. Even the time-release form of melatonin does not reproduce normal cycles." Bottom line: Your body makes it's own supply of melatonin, so create the right setting for sleep and train your body clock for a regular sleep cycle.

Choose a Good Sleep Lifestyle
If your dream bank is almost empty, and your pillow offers no rest, you can take some action to create better conditions for a full night of sleep. You can try using a sleep mask or blackout curtains, and arrange your bedroom for optimal comfort to promote consistent sleep. If you're watching television or hovering over your computer right up until bedtime, you may be sabotaging your chances of getting to sleep easily. Get a handle on your habits and then make a plan for improving your bedtime routine.

Next: Tips For Improving Your Sleep