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Underweight

"You can never be too rich or too thin". This quote is credited to the Duchess of Windsor, Wallis Simpson. While this may have been cause enough for King Edward VIII to abdicate his throne for her, studies are showing that being too thin can be harmful to your health.

The adverse consequences of obesity are well known. The higher occurrences of heart disease, cancer, stroke, hypertension, diabetes, and numerous other co-morbidities have doctors encouraging patients to lose weight. However, there is a point where being chronically or significantly underweight can also have risks. Aside from eating disorders, such as anorexia or bulimia, which are well-recognized causes of mortality, what is the risk in being too thin?

The good news with those who are underweight is that most people up until middle age have no problems with a slighter than normal build, especially if it is consistent and not associated with a chronic disease. The protective value appears to wear off in time until age 65, when chronic problems may set in. Being underweight is associated with fertility issues in both men and women and "critical mass" is necessary for proper ovulation and sperm production. Thinner also means less dense and more brittle bone structure, an increased risk of type 2 diabetes, higher fats in the blood (perhaps from more rapid metabolism), and a higher risk (according to the Journal of Public Health) of accidents and depression. This also assumes that underweight does not occur because of poor or improper nutrition, which also carries its own set of risk factors for the body.  

As the body ages, there is an increased risk for falls and fractures, since supporting tissue for the bones is limited. A rapid metabolism may have other primary causes, such as hyperthyroidism or diseases with increase bone turnover. An increased vulnerability to infection and a compromised immune system have also been reported.

Underweight is measured according to universally available BMI charts (body mass index, which is calculated through height and weight measures). Generally, underweight is associated with a BMI between 18.5 and 19 (normal BMIs are between 19 and 25). In more recognizable terms, a woman 5'9" or more is considered underweight if she is less than 112 pounds and a woman that is 5'2" and less than 90 pounds is also considered underweight. These are extrapolated to use for men (6'1" and 126 pounds might be considered pathologic in a male, but extremely slim yet acceptable in a female), and in those under the age of 20. Low mortality is actually found in normal to 10 percent underweight until older ages when illness or loss of musculature makes it more of a risk factor.

Most concerning is a loss of weight from normal to underweight. Poor nutrition or eating disorders are more common in the young, but cancer is a particularly dreaded cause as age increases. Intestinal malabsorption, endocrine disorders such as diabetes or hyperthyroidism, depression, and even alcohol abuse are common offenders of decreasing weight in adults. Someone's diet which is going "too well" or perhaps even too easily may also have a less desirable cause associated with it.

Doctors look for a current height and weight, documentation of any changes in the last year and reasons for that, and any complications that may be associated with the loss of weight, from chronic infections to loss of appetite or falls. Any unintended weight loss should have all causes investigated to insure good health. Perhaps it is best said that too much of any condition can have its own unintended consequences.


Authored by Dr. Bob Goldstone, M.D.

The information contained on this page is not intended to provide medical advice, which should be obtained directly from your physician.