Anxiety disorders have been linked to several different physical illnesses, but the age old question of which comes first, the chicken or the egg, continues to be debated. In some cases, the stress of living with a chronic illness can lead to anxiety. On the other hand, there are some physical illnesses that can develop because of living with chronic stress.
Some illnesses, such as heart disease, thyroid disease, cancer and high blood pressure are more prevalent in individuals with anxiety according to a 2006 study completed at the University of Manitoba. This study looked at over 4,000 patients previously included in the German Health Survey.
The study showed a higher rate of anxiety in participants that suffered from a physical illness but even higher rates showed in those with respiratory and gastrointestinal diseases, arthritis, allergies, thyroid diseases and migraine headaches. Those individuals with both a physical illness and an anxiety disorder were found to have more days of disability than those with only one or the other. 
One concern of medical professionals is the effect on the physical illness when anxiety goes undetected and untreated. An article in Harvard Health Publications states, "When people with these disorders have untreated anxiety, the physical disease is more difficult to treat, symptoms often become worse, and in some cases, they die sooner." 
Doctors often screen and are on the lookout for depression in patients with chronic diseases and may refer these patients to therapists or other mental health providers to help cope with the long-term effects of these illnesses. It has only been recently, however, that researchers looked into the link between anxiety disorders and physical illnesses.
Complicating the matter further is the fact that anxiety disorders often have physical symptoms. Anxiety itself can lead to headaches, gastrointestinal issues, chest pains, palpitations, trouble swallowing and other physical ailments. Many individuals with anxiety first go to the doctor, not for anxiety, but for the physical symptoms they are experiencing. Anxiety may be diagnosed only after your doctor can find no physical cause for the symptoms.
Researchers are concerned because in the studies on anxiety and illness, it became apparent that those who suffered from anxiety had a much more difficult time managing symptoms of their illness and suffered from a poorer quality of life. With almost one-third of those with an anxiety disorder never receiving treatment, many people are suffering from worsening symptoms of their physical illness. For patients who receive care for physical illness but are still experiencing symptoms such as dizziness, insomnia, headaches, gastrointestinal issues or other physical symptoms associated with anxiety, it may be beneficial to speak with your doctor about an underlying issue of anxiety or depression. Treating both the physical illness and the anxiety disorder can help to create a better quality of life and help you better manage your physical and emotional symptoms.
 "Anxiety Disorders Linked to Physical Conditions," 2006, Oct 24, Staff Writer, ScienceDaily.com
 "The Link Between Anxiety and Physical Illness," 2008, Aug 5, Staff Writer, Harvard Health Publications
"Separating Anxiety From Physical Illness, 2008, March 18, Patricia Hentz, The Clinical Advisor