The media may glorify rail-thin actresses and size 0 models, but being underweight, which means a body mass index below 18.5, is a serious matter with distinct health consequences. Nutrient deficiencies, impaired immunity and hormonal problems are the three top health risks associated with being underweight, but there are many others, including an increased risk of death. If you are underweight, consult a healthcare professional to help you craft a weight-gain plan and make sure you do not have an underlying medical condition.
Danger of Nutrient Deficiencies
Use a BMI calculator to help you quickly determine if you are underweight for your height. Ideally, your BMI should be between 18.5 and 24.9.
When you have a below-normal BMI, you're probably not eating enough calories to maintain a healthy weight, which puts your body at risk for deficiencies in nutrients that support overall good health. A lack of calcium and vitamin D in the diet, for example, can lead to fragile bones and osteoporosis, a condition in which your bones weaken and can fracture easily. Deficiencies in iron, folate and vitamin B-12 can cause anemia; when you're anemic, you may experience dizziness and low energy. Too little vitamin C can result in problems with your connective tissues, resulting in gum disease and loss of teeth; you may also be unable to heal properly from wounds and burns. A deficiency in vitamin A can lead to dry, discolored skin and hair, brittle fingernails, and vision problems.
A weakened immune system is another top health risk associated with an underweight condition. When you don't get enough nourishment, you'll lack energy for everyday activities, and your body won't have enough of certain nutrients, such as protein and antioxidants, that strengthen your immune function. Protein is needed to make hormones and enzymes, and it's critical for healing wounds and synthesizing cells that fight infection. Dietary antioxidants do battle with free radicals in your body, molecules that can damage your DNA and lead to premature aging and abnormal cell development. With low levels of immune-boosting antioxidants like vitamins A, C and E, and the minerals zinc and selenium, your body has difficulty fighting off common conditions, like colds and flu, as well as other types of infections. You may also be at a higher risk for life-threatening diseases like cancer.
Female Reproductive Issues
A top health risk for underweight women is reproductive problems. Being underweight causes hormonal imbalances that may halt or disrupt the menstrual cycle. Women with a below-normal BMI may find it more difficult to get pregnant, sometimes taking a year or more to do so. If underweight women are able to conceive, they are 72 percent more likely to have a miscarriage in the first trimester, reports the European Food Information Council. Low-BMI women are at greater risk of delivering premature or underweight babies, says BabyCenter.
Other Top Health Risks of Being Underweight
Being underweight can have other health risks as well, including death. Underweight adults are as much at risk of death as those who are overweight, according to a meta-analysis published in the Journal of Epidemiology and Community Health in 2014. By looking at the results of 51 studies overall, the authors found that low-BMI people were 1.8 times more likely to die than those with a normal BMI.
An underweight condition may also be a sign of an underlying emotional or mental disorder, like anorexia nervosa. Anorexia carries its own health risks; along with those noted above, other issues include stunted growth in young women, muscle wasting, constipation, low blood pressure, and even brain damage.
- CDC: About Adult BMI
- FamilyDoctor.org: Healthy Ways to Gain Weight if You’re Underweight
- Merck Manual: Vitamin C Deficiency
- Medscape: Vitamin A Deficiency
- Academy of Nutrition and Dietetics: Protect Your Health with Immune-Boosting Nutrition
- YourFertility.org: Fertility and a Woman’s Weight
- European Food Information Council: Underweight Women at Greater Risk of Miscarriage
- BabyCenter: Pregnant and Underweight
- ScienceDaily: Underweight People at as High Risk of Dying as Obese People, New Study Finds
- NIH: Eating Disorders
- NIH: Calculate Your Body Mass Index