Not so long ago, researchers often excluded women from medical studies or included only a small number.  Today, more emphasis is being placed on examining how diseases, medications, alcohol and tobacco, and other health-related concerns specifically affect women.

This has resulted in greater knowledge about how important it can be to understand the differences between women and men when trying to prevent health problems, recognize diseases, and treat or manage illnesses.  Many medical problems disproportionately affect women; and it has become clear that diseases that were once strongly identified with men are not restricted to one sex.  Look at the statistics relating to some of today’s most common diseases and conditions:

• Cancer.  It’s no surprise that cancer affects both sexes.  With women, breast cancer often takes center stage.  Although breast cancer is a major cause of death in U.S. women, it comes in second to lung cancer and not too far ahead of colorectal cancer.

• Alzheimer’s disease.  More women than men develop Alzheimer’s disease, in part because women live longer.  The disease is responsible for the deaths of nearly 42,000 women each year.  That’s more than twice the number of men.

• Cardiovascular disease (CVD).  CVD is the leading killer of American women and men—who both experience heart attack, stroke and congestive heart failure.  Women account for 53 percent of all CVD deaths in the U.S.

• Irritable bowel syndrome (IBS).  Two to three times as many women as men have IBS. The disorder is characterized by abdominal pain or cramping and bowel function changes—including bloating, gas, diarrhea and constipation.

• Fibromyalgia.   Between 80 percent and 90 percent of the 3 million Americans affected by fibromyalgia are women.  This chronic condition is characterized by fatigue, widespread pain in the muscles, ligaments and tendons, and multiple tender points on the body

• Osteoporosis.  About 8 million American women have osteoporosis while only about 2 million American men are affected.  Bone fractures—the most frequent complication of osteoporosis—is about twice as common in women as they are in men.

• Autoimmune diseases.  Women are almost three times more likely than men to have an autoimmune disease—a disorder that occurs when the body produces an immune response against its own tissues.  There are more than 80 autoimmune diseases.  To name just a few:

                 Graves’ disease is the most common cause of overactive thyroid.  Women to men: 7 to 1.

                 Rheumatoid arthritis.  Women to men: 4 to 1.

                 Hashimoto’s disease. causes thyroid gland inflammation.  Women to men: 50 to 1.

                 Multiple sclerosis.  Women to men: 2 to 1

• Headaches.  More than 80 percent of women of reproductive age have headaches.  Not only do women get headaches more often than men do, but they also experience more severe headache symptoms.  Three times as many women as men get migraine headaches.

Sex hormones and reproductive organs are not the only way to describe how women and men differ physiologically.  Although we share much of the same anatomy, medical research is finding that key body parts and systems don’t always develop or function in the same way, which may explain why the sexes often experience diseases differently.

Your immune system contributes to the development of lymphocytes, white blood cells that play a major role in protecting your body against bacteria or viruses.  Compared with men, women have greater numbers of certain lymphocytes, which gives women greater resistance to certain types of infection.  But it may make them more susceptible to immune system malfunctions.

Autoimmune diseases have no clear cause.  Some can run in families, suggesting that there’s a genetic component.  But because so many autoimmune diseases affect women more than men, researchers have investigated how sex hormones play a role in how immune cells are activated and behave.

Women tend to develop diseases of the heart and blood vessels about 10 years later than men.  Studies mainly attribute this difference to the protection provided by estrogen until the time of menopause.

Postmenopausal women also tend to experience an increase in blood pressure.  Before age 55 a greater percentage of men than of women have hypertension.  After age 55, the percentage of women with hypertension outnumbers that of men.

In addition, heart disease is more often fatal in women than in men.  This may be because women are older and have other health complications at the time of diagnosis.  Heart disease in women also can be more difficult to diagnose.  Instead of chest pains, a woman may experience shortness of breath, dizziness and nausea, all of which may be mistakenly attributed to other causes, rather than to a heart problem.

Your brain contains billions of nerve cells (neurons) that coordinate thought, emotion, behavior, movement and sensation.  Researches have found that the brain anatomy of women and men are not identical, as previously thought.  Instead, there are differences in size and shape, and in the number and distribution of neurons, causing differences between the sexes in cognitive function and receptivity to disease.

Men’s and women‘s bones reach their peak mass between ages 25 and 35.  After that, they decline slightly in both size and density.  However, women experience a loss in density at a faster rate than men do.

Some differences have been found in the digestive systems of women and men. -- Generally, food takes longer to pass through the gastrointestinal tract of a woman, so many women may have more problems than do men with abdominal bloating and gas.  --The hormonal changes that occur during the menstrual cycle and pregnancy can affect the muscle contractions that move food from your stomach to your intestinal tract and rectum. --The composition of bile, which facilitates the digestion of fats in the small intestine, is influenced by the amount of estrogen and progesterone in the body.  Researchers have found the gallbladder is slower at emptying bile into the digestive system when women are ovulating and during pregnancy when progesterone levels are high.

Once drugs enter the blood stream, women’s and men’s bodies can react much differently.  One study found women wake up twice as fast from anesthesia as men do.  Another study discovered a class of painkillers called kappa opioids appeared to be about twice as effective in women as in men.  Most recently, a study found women over age 45 who took low-dose aspirin for 10 years didn’t lower their risk of heart attack, but did experience some protection against stroke.  A similar study done years earlier on men found the exact opposite to be true—aspirin use reduced men’s heart attack risk, but didn’t have an impact on stroke rates.

There are more differences, too, such as the way women and men handle alcohol, tobacco and drugs, and the way each experiences pain.

In 1988, the Food and Drug Administration (FDA) ruled that drugs intended for women had to be tested in women before they could be approved for distribution and sale.  Five years later, the FDA released specific guidelines for evaluating sex differences in how drugs were to be tested.  A subsequent regulation in 1998 required that safety and effectiveness data on drugs had to be presented separately for men and women in new drug applications.

Despite these advances, the number of women involved in initial, small-scale safety studies, which measure how participants absorb, metabolize and excrete a drug to set dosing levels for later trials, still appears to include too few women.  In fact, according to a 2001 report by the U.S. General Accounting Office, women represented only 22 percent of the participants in initial, small-scale safety studies, but made up more than half of the participants in the later, larger trials.  That may be why the majority of prescription drugs withdrawn from the U.S. market between 1997 and 2000 were withdrawn because of side effects in women.

Research is confirming that women and men are different in ways that go beyond reproductive systems and hormones.  This has helped pave the way for an entirely new appreciation for gender-based medicine.  In the future, gender-based differences are expected to gain further attention in medical investigations.  The future holds the promise of unique prevention, diagnostic and treatment strategies targeted specifically to women.