General Adverse Effects of Obesity
Over 300,000 lives could be saved each year if all Americans maintained a healthy weight. Obesity is associated with more chronic health problems than smoking, heavy drinking, or being poor. And next to smoking, obesity is the most common preventable cause of death in the US. According to one 2001 study, even being overweight increased the risk for diseases. In this 10-year study, the risks for developing diabetes, gallstones, hypertension, heart disease, stroke, and colon cancer rose proportionally with the degree to which the individuals were overweight.
Some studies indicate that the following:
- The lowest risks for heart disease, diabetes, and some cancers are in people with body mass index (BMI) values of 21 to 25.
- The risks increase slightly when BMI values are between 25 and 27.
- They are significant in BMIs between 27 and 30.
- They are dramatic over 30. [For calculating the BMI, see box Calculating Body Mass Index (BMI)]
Anyone with chronic health problems (eg, heart or lung disease, stroke, or arthritis) or risk factors for them must be concerned about extra weight. In general, obesity may contribute to disease in several ways:
- Metabolic Changes. As fat stores increase, the fat cells themselves enlarge and produce a number of chemicals that increase the risk for a number of diseases. Such diseases may include diabetes, high blood pressure, gallbladder disease, and some cancers.
- Increased Mass. The increased body weight itself causes structural problems that cause injury and diseases, including osteoarthritis and sleep apnea. One can argue that this increased mass is associated with psychological disorders, particularly depression, which is now a known health risk.
- Harmful Fat Cell Types. Weight concentrated around the abdomen and in the upper part of the body poses a higher health risk than fat that settles in a pear-shape around the hips and flank. Fat cells in the upper part of the body appear to have different qualities from those found in the lower parts.
Experts are still debating, however, about the degree to which being overweight hurts healthy people with no risk factors for serious illnesses. Some argue, in fact, that in anyone who is not severely obese (BMI over 30), it is an unhealthy diet and sedentary lifestyle that causes harm, not weight per se. In support of this argument, a British study found that overweight fit individuals had half the death rate of unfit trim individuals. In any case, actual obesity is known to be harmful, and eating healthy foods and exercising are essential in any case and usually lead to weight loss.
Individuals with a BMI of at least 30 have a 50% to 100% increased risk for death compared with individuals at a BMI of 20 to 25. Mortality rates from many causes are higher in obese people, but heart disease is the primary cause of death. People who are obese have almost three times the risk for heart disease as people with normal weights. Being physically unfit adds to the risk.
Weight concentrated around the abdomen and in the upper part of the body (apple-shaped) is particularly associated with insulin resistance and diabetes, heart disease, high blood pressure, stroke, and unhealthy cholesterol levels. Fat that settles in a “pear-shape” around the hips and flank appears to have a lower association with these conditions.
Obesity poses many dangers to the heart.
Damage in the Blood Vessels. Studies are reporting higher levels of a factor called C-reactive protein, which is a marker for inflammation and damage in the arteries from an over-active immune response. Changes in body fat as people age, particularly increasing abdominal fat, have specifically been associated with stiffness in the aorta, the major artery leading from the heard.
High Blood Pressure. Hypertension is the health problem most commonly associated with obesity, and the greater the weight, the greater the risk. While hypertension carries its own serious risks for stroke and heart attack, overweight people with high blood pressure are also at increased danger for enlargement of the left heart chamber, a major risk factor for heart failure. The link between obesity and high blood pressure is complex and may reflect interactions of genetic, demographic, and biologic factors. Many studies have reported that modest weight loss is beneficial for reducing existing blood pressure and the risk for heart failure. [For more information, see the Well-Connected Report #14 , High Blood Pressure .]
Unhealthy Cholesterol Levels and Lipid Levels. The effect of obesity on cholesterol levels is complex. Although obesity does not appear to be strongly associated with cholesterol levels, among obese individuals triglyceride levels are usually high while HDL (the so-called “good” cholesterol) levels tend to be low, both risk factors for heart disease.
Stroke. Obesity is also associated with a higher risk for stroke.
Insulin Resistance and Type 2 Diabetes
Most people with type 2 diabetes are obese and, in fact, losing weight can help prevent its development. It should be noted that only a minority of obese people is diabetic. Nevertheless, researchers have blamed obesity and sedentary living for the dramatic increase in type 2 diabetes over the past years.
People with type 2 diabetes have abnormalities that produce an inability to use insulin, a critical hormone in the metabolism of sugar. This condition, called insulin resistance , and has effect of increasing blood glucose (sugar in the blood), the hallmark of diabetes. (Insulin resistance is also associated with high blood pressure and abnormalities in blood clotting.)
Although the exact mechanisms of the relationship between obesity and diabetes type 2 is still not entirely clear, fat cells may release certain chemicals that inhibit the body’s sensitivity to insulin.
Obesity has been associated with certain cancers, and some experts believe that effective weight control for children and adults could reduce cancer rates by 30% to 40%.
Uterine Cancers. Women who are obese appear to have two to three times the risk for uterine cancer as thinner women.
Prostate Cancer. A Western lifestyle is associated with prostate cancer, although direct causal role for either obesity or dietary fats has not been established. A 2001 study did find obesity to be associated with a modest increase in prostate cancer mortality, although not with the risk for prostate cancer itself. In a previous study of Chinese men, however, it was not obesity itself but an unhealthy fat distribution that was associated with a higher risk. High risk individuals in the study were those whose fat was more centered in the abdomen, the so-called apple-shape. Either one or both of the hormones that are associated with both obesity and diabetes, , leptin and insulin, could theoretically stimulate prostate cancer growth.
Breast Cancer. Studies have reported mixed effects on the association between obesity and breast cancer. A number of studies have linked obesity to breast cancer in postmenopausal women, particularly in women who begin to gain weight after age 18. One study in fact suggested that being heavier as a child conferred a lower risk for breast cancer after menopause.
Gallbladder Cancer. Obese women are at higher risk for gallbladder cancer.
Gastrointestinal Cancers. A number of cancers in the gastrointestinal tract have been associated with obesity:
- Cancer of the esophagus. The increased risk may be due to a higher incidence of gastroesophageal reflux disorder (heartburn) in people who are overweight.
- Colon cancer. There is a demonstrated link between increased body mass and colon cancer risk for both men and women.
- Pancreatic cancer. One study has linked obesity to pancreatic cancer, but also found that overweight patients who are physically active have a lower risk.
(Obesity does not appear to be related to a higher risk for stomach cancer.)
Muscles and Bones
Effects of Weight on Muscles and Bones. Obesity places stress on bones and muscles, and overweight people are at higher risk for hernias, low back pain, and aggravation of gout and other arthritic conditions. Studies report that the incidence of osteoarthritis is significantly increased in people who were overweight. People who are obese are also at higher risk for carpal tunnel syndrome and other problems involving nerves in their wrists and hands. It should be noted that some weight may be protective against osteoporosis (loss of bone density).
Osteoporosis. Some extra weight is beneficial for maintaining bone density in women after menopause. Before menopause, however, overweight women who lose weight and who also increase their intake of dietary calcium are not at risk for bone loss.
Eyes and Mouth Disorders
Obesity increases the risk for the following mouth and eye disorders:
- Gum disease.
- Cataracts. A study of 17,150 men concluded that there is a higher association between cataracts and greater body mass, height, and carrying fat around the abdomen.
- Maculopathy. Maculopathy is an eye disease related to aging. Obesity also appears to be related to this disease.
Reproductive and Hormonal Problems
Infertility. Abnormal amounts of body fat, either 10% to 15% too high or too low, can contribute to infertility in women. Obesity is specially related to certain problems related to infertility, such as uterine fibroids or menstrual irregularities. In men, obesity can contribute to reduced testosterone levels.
Effect on Pregnancy. The dangerous effects of obesity on pregnancy are multifold. They include high blood pressure, gestational diabetes (diabetes, usually temporary, that occurs during pregnancy), urinary tract infections, blood clots, prolonged labor, a higher fetal mortality rate in late stages of pregnancy, and cesarean delivery. Infants of women who are obese are also at higher risk for neural tube birth defects, which affect the brain or spine. Folic acid supplements, ordinarily effective in preventing these conditions, may not be as protective in overweight women.
Effects on the Lungs
Obesity is thought to be a risk factor for adult-onset asthma, although there is some evidence that although obesity causes wheezing and shortness of breath it does not appear to be strongly associated with the disease mechanisms in the lungs that cause true asthma.
Obesity also puts people at risk for hypoxia, in which oxygen is insufficient to meet the body’s needs. Obese people need to work harder to breathe and tend to have inefficient respiratory muscles and diminished lung capacity. The Pickwickian syndrome, named for an overweight character in a Dickens novel, occurs in severe obesity when lack of oxygen produces profound and chronic sleepiness and, eventually, heart failure.
Effect on the Liver
Hepatitis. People with obesity and diabetes type 2 are at higher risk for a condition called nonalcoholic steatohepatitis (NASH), liver damage that is similar to liver injury seen in alcoholism. In some cases it can be very serious and require liver transplantation.
Gallstones. The incidence of gallstones is significantly higher in obese women and men. The risk for stone formation is also high if a person loses weight too quickly. In people on ultra-low calorie diets, gallstones may be prevented by taking ursodeoxycholic acid (Actigall).
People who are obese and nap tend to fall asleep faster and sleep longer during the day. At night, however, it takes them longer to fall asleep and they sleep less than people with normal weights. In an apparent vicious circle, studies have suggested that not only can obesity interfere with sleep, but that sleep problems may actually contribute to obesity.
Sleep Apnea. Obesity, particularly the apple-shape, is particularly associated with sleep apnea, which occurs when the upper throat relaxes and collapses at intervals during sleep, thereby temporarily blocking the passage of air. It is increasingly being viewed as a potentially serious health problem, including heart disease and stroke. Some studies in fact suggest that among overweight people, those who have sleep apneas have a greater heart risk than those without them. Obesity may contribute to sleep apnea simply by fatty cells infiltrating the throat tissue, which could narrow the airways. In one study, the more obese a person with sleep apnea was, the higher the pressure on the airway and therefore the greater the obstruction of the airway. (Obstructive sleep apnea may also cause obesity itself, however, as sleepy people tend to be sedentary.) Some studies are even indicating that treating sleep apnea may even help people lose abdominal fat.
Narcolepsy. A small European study found a link between narcolepsy (a sleep disorder characterized by excessive daytime sleepiness with frequent daily sleep attacks) and high BMI.
Emotional and Social Problems
A study that followed obese adolescents for seven years found that, compared to thinner peers, overweight girls completed fewer years of school, were 20% less likely to be married, and had 10% higher rates of household poverty. A 2000 study of third graders found a direct relationship between depressive symptoms and body mass index in girls, but not boys. Women and girls tend to blame themselves for being heavy while males tend to attribute being overweight to outside factors. Studies consistently show that overweight males (both boys and men) are not as severely emotionally affected as females of any age. Nevertheless, in the first study mentioned above, 11% of obese men were less likely to be married than non-obese men and their incomes were lower.
No evidence exists, however, that obese people suffer from emotional disorders, such as major depression or anxiety, to any greater degree than thinner people. Generally, depression and anxiety are caused by the weight problem and are usually resolved by weight loss.
Revision date: July 6, 2011
Last revised: by Janet A. Staessen, MD, PhD