Maintaining a healthy body weight is important for avoiding many diseases, but a new study from the Massachusetts Eye and Ear Infirmary (MEEI) finds that for primary open-angle glaucoma (POAG), one of the most common age-related eye diseases, the picture may be more complex. A large, prospective MEEI study, conducted over 20+ years, found that higher body weight (specifically, body mass index, BMI) is not associated with higher risk of POAG. In fact, the research shows that in women, higher BMI is significantly linked to reduced risk for a variant of POAG known as normal tension glaucoma (NTG). The researchers, led by Louis R. Pasquale, MD (pictured), say that clinicians and patients should be cautious about these findings until further research provides substantiation and clarifies the related biological mechanisms.
Glaucoma is a complex, potentially blinding illness that damages the optic nerve, and POAG is the most common type. Elevated eye pressure (intraocular pressure, IOP) is strongly linked to optic nerve damage. Effective treatments to control IOP are available to help glaucoma patients preserve their best possible vision. But in people with NTG, optic nerve damage occurs even though their IOPs are not elevated, as defined by accepted standards. Diagnosing and treating NTG presents special challenges for eye M.D.s (ophthalmologists) and patients.
"Understanding the mechanisms that drive BMI and other body composition factors in relation to POAG might help us solve some mysteries connected with this complex illness," Dr. Pasquale said. "It's reasonable to speculate that hormonally-controlled factors released from adipose or lean tissues may alter the risk of NTG in women. Higher BMI in postmenopausal women is linked with higher estrogen levels, which might positively affect estrogen receptors in the optic nerve," he explained.
BMI refers to the body's adipose (fat) content in relation to lean body mass tissues (muscle, fluid, bone, and other non-fat tissues). When a person has a "higher BMI," that means the person's body includes more fat than the normal standard for his or her age.
The study participants were 78,777 women enrolled in the Nurses Health Study (1980 through 2004) and 41,352 men enrolled in the Health Professionals Follow-up Study (1986 through 2004). In women, each unit increase in BMI was associated with a 6 percent reduction in risk for NTG (defined as IOP equal to or less than 21 mmHg at the time of diagnosis of POAG). Also, in women, having higher BMI during the young adult years was associated with reduced risk of NTG. In men, BMI was not associated with POAG. Because the ethnicity of most participants was European-Caucasian, the study's implications may be limited to similar patient populations.
Dr. Pasquale suggested that if the relationship of POAG to BMI and related body-composition factors can be clarified in future research, new treatments could be developed for patients with POAG, particularly those who have the normal tension variant of the disease.
Illustration: Massachusetts Eye & Ear Infirmary.
American Academy of Ophthalmology News Release (08/02/10)
Medical News Today (08/03/10)
Science Daily (08/04/10)
Abstract (Ophthalmology; 117(8), 1521-1529 (08/10))