Maintaining a low Body Mass Index, or BMI, has long been considered a healthy practice for the general population, but two new studies have suggested links between low BMI and serious health conditions.
The first study, published in the journal Neurology found that older people in the earliest stages of Alzheimer's disease are more likely to have lower BMI.
"The earliest stages of Alzheimer's are associated with some metabolic dysfunction, as evidence with the differences in BMI," said Dr. Jeffrey Burns, lead author of the study and director of the Alzheimer and Memory Program at University of Kansas Medical Center. "We saw the relationship between Alzheimer's markers with body composition with low BMI in people in the earliest stages of the disease, both in people with mild cognitive impairment and in people without functional problems."
While Burns said he does not have the evidence to support whether low BMI puts people at risk of cognitive impairment or cognitive impairment may contribute to lower BMI, he said it goes beyond simple changes in one's ability to remember to eat.
"It reflects there is a systemic response to an underlying problem," said Burns. "We think of Alzheimer's as classically a brain disease, but now there's evidence that there are measurable changes going on in the body."
BMI is a number calculated from a person's height and weight that is meant to indicate body fatness in most people. According to the Centers for Disease Control and Prevention, 18.5 and below is considered underweight. Normal weight ranges from 18.5 to 24.9. Overweight spans from 25 to 29.9 and obese is considered 30 and above.
Researchers analyzed more than 500 patients with Alzheimer's biomarkers through advanced brain imaging techniques and cerebrospinal fluid. The biomarkers are often present years before symptoms set in. Study participants included people without any memory problems and those with mild cognitive impairment.
While the link between later-life low body mass and Alzheimer's disease has been fairly established by previous research publications, William Thies, chief medical and scientific officer of the Alzheimer's Association, said this study appears to extend this relationship to the earliest stages of Alzheimer's pathology through the biomarker findings.
Interestingly, prior research has shown that middle-aged people who are overweight or obese (higher BMIs) are at greater risk of developing Alzheimer's disease.
"It appears that mid-life high BMI and later life lower BMI are both related to Alzheimer's disease," said Thies. "Perhaps the mid-life findings are due to exacerbation of vascular risk by high BMI. The later-life linkage between low BMI and Alzheimer's may come about as the result of the earliest changes of Alzheimer's disease and result in a lowering of appetite, among other things."
While Burns said they are currently conducting studies that look deeper into metabolic changes in the body and brain, Thies said further research on early-stage symptoms is expansive and expensive.
"Without more money being invested in basic Alzheimer's disease research studies, we will never know the real relationship between BMI, age, and Alzheimer's disease," said Thies. "We must see, and quite soon, a greater commitment to Alzheimer's disease research at the federal level, and from industry, and from the American public."
In the second study, low BMI was spotlighted as increasing risk of death within 30 days of surgery. The research, published in the Archives of Surgery, found that, of the nearly 190,000 patients included in the study, 1.7 percent of them died within 30 days of surgery. Deaths among patients with a BMI less than 23.1 were twice that of patients with a BMI of 35.3 or higher.
"Patients with low body mass index are at significantly higher risk of death with 30 days after following general and vascular surgical procedures," said Dr. George Stukenborg, associate professor of public health sciences at University of Virginia's School of Medicine. "Low BMI should be taken into account as an important risk factor for risk of death within 30 days of the procedure."
Oddly, patients in the heavier BMI groups did not have "a statistically significant mortality risk," said Stukenborg.
Patients who underwent laparatomy, or a procedure involving a large incision through the abdominal wall, were at highest risk of death after surgery, compared witho other operations.
Stukenborg said the research does not disclose why BMI is a risk factor for death, but experts say the higher amount of deaths could be among the frail and elderly, not the young, thin and healthy. Stukenborg said he and his colleagues plan to investigate reasons for the increased risk in upcoming studies.