Young premenopausal women with excessive amounts of visceral fat are at increased risk for osteoporosis, according to new research presented at the Radiological Society of North America 96th Scientific Assembly and Annual Meeting. For years, it was believed that obese women had a lower risk of developing osteoporosis and that the mechanical loading from excess weight was good for their bones. It now appears that having too much fat, particularly deep abdominal fat, might be damaging to bone health, Miriam A. Bredella, MD, from Massachusetts General Hospital and Harvard Medical School, Boston, told meeting attendees. “With this ongoing obesity epidemic, we were actually seeing more and more young women breaking their forearms or their wrists, and the single biggest risk factor in this group was actually increased body weight,” she told Medscape Medical News. “We thought we should look take a closer look at whether obesity really did protect against osteoporosis.”
Dr. Bredella and her team studied 50 premenopausal women whose mean body mass index was 30 kg/m2 (range, 19 to 46). The women underwent assessment of L4 bone marrow fat with magnetic resonance (MR) spectroscopy as a measurement of lumbar bone density. In addition, abdominal subcutaneous, visceral, and total fat depots and trabecular bone mineral density of L4 were assessed using quantitative computed tomography. “Using MR spectroscopy was a new thing that we did in this study. MR spectroscopy is a technique that is more sophisticated than the regular bone density test. It does not involve radiation,” Dr. Bredella explained. “With this test, we could actually look inside the bones and see how much fat was in the bones.”
These examinations revealed an inverse association between visceral fat and bone mineral density (r = –0.31; P = .03) and between vertebral bone marrow fat and bone mineral density (r = –0.45; P = .001). The researchers also found that there was a positive correlation between bone marrow fat and visceral fat (r =.28; P = .04) that was independent of bone mineral density.
However, there was no significant correlation between either subcutaneous fat or total fat and bone marrow fat or bone mineral density. “The more deep belly fat you have, the more fat you have in your bones, and the more fat you have in the bones, the weaker they will be,” Dr. Bredella said. “All things being equal, if you have 2 obese women and one has a lot of deep belly fat and the other one has exactly the same weight but her fat is distributed more superficially around the hips and thighs, then the woman with the deep belly fat will have weaker bones.”
She suggested that belly fat weakens bones because this type of fat secretes adipokines, which weaken bones. “It is important for people to be aware that obesity is a risk factor for more than diabetes and cardiovascular disease,” she said. “Now they need to know that excess belly fat is a risk factor for bone loss.”
Radiological Society of North America (RSNA) 96th Scientific Assembly and Annual Meeting: Abstract SSJ17-05. Presented November 30, 2010.
Experts have suggested that an intensive lifestyle intervention helps individuals with type 2 diabetes lose weight and keep it off, along with improving fitness, control of blood glucose levels and risk factors for cardiovascular disease. Improving blood glucose control and cardiovascular risk factors in patients with type 2 diabetes is critical in preventing long-term complications of the disease.
The Look AHEAD (Action for Health in Diabetes) Research Group conducted a multicenter randomized clinical trial comparing the effects of an intensive lifestyle intervention to diabetes support and education among 5,145 overweight individuals with type 2 diabetes.
Of these, 2,570 were assigned to the lifestyle intervention, a combination of diet modification and physical activity designed to induce a 7 percent weight loss in the first year and maintain it in subsequent years. The 2,575 individuals assigned to the diabetes support and education group were invited to three group sessions each year. On average, across the four-year period, individuals in the lifestyle intervention group lost a significantly larger percentage of their weight than did those in the diabetes support group.
They also experienced greater improvements in fitness, hemoglobin A1c level (a measure of blood glucose), blood pressure and levels of high-density lipoprotein. Individuals in the diabetes support group, on the other hand, experienced greater reductions in low-density lipoprotein, owing to greater use of cholesterol-lowering medications in this group.
The report was published in the September 27 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.
In an earlier investigation, the researchers had looked at the hormonal effects of diet cola ingestion on parathyroid hormone, calcium, phosphorus, insulin, alkaline phosphotase, and ghrelin.
The researchers thought that because of the phosphorus load, PTH would surge, but they found exactly the opposite, “which was that it comes down and sort of comes back to baseline; alkaline phosphatase increases also,” Larson said. “We thought, 'Well, that suggests there's some turnover of bone going on, and maybe there's some calcium being mobilized and it's going out in the urine and that might partially account for the fracture risk and decreased bone density that's being described.”
With results from that earlier study as the impetus, Larson and colleagues undertook the current study, for which they recruited 20 healthy women, ages 18 to 40.
Exclusion criteria were fracture within the prior six months, known bone disease or vitamin D deficiency, steroid or diuretic use, breast-feeding, and vitamin D supplementation above the current U.S. recommended daily allowance.
The participants were randomized to drink 24 ounces of either water or diet cola on two study days. Urine was collected for three hours after ingestion of the designated beverage and assayed for calcium, phosphorous, and creatinine using standard assays.
Data were analyzed on 16 participants; four were excluded because of lab error or failure to comply with the study protocol, the researchers said.
In addition to the higher calcium and phosphorus excretion, the investigators also found that normalized calcium and phosphorous excretion per gram of creatinine showed a trend in the same direction as total calcium and phosphorous per three hours. That figure did not achieve statistical significance, however.
Although the study was small, “it does look like there was a statistically significant rise in urine calcium,” said Larson. “The important part about that is that Diet Coke has no calcium content.”
Compared with milk, which also causes a rise in urine calcium but is replacing calcium at the same time, diet colas “would [create] an overall negative body calcium balance and that could partially explain why they appear to be bad for bones,” she said.
Although the study is too small to draw any firm conclusions, “certainly my personal practice among adolescent girls who tend to be concerned about their weight — and who drink diet beverages while they are in that critical period of bone formation — is to just try and counsel them to set habits of drinking calcium-containing beverages and maintaining adequate vitamin D,” said Larson.
Elizabeth Barrett-Connor, MD, of the University of California San Diego, called the study “fabulous.”
Barrett-Connor, who was not involved in the study, said that although it was a small and short-term trial, “it fits with all my preconceived ideas” about the nutritional problems with diet soda. “This [is new] but it just makes sense.”
The study was funded by the Walter Reed Department of Clinical Investigations.
The researchers also looked at bone density and structure in the lower leg in around 360 19-year-old men who had previously done sports but had now stopped training. They found that men who had stopped training more than six years ago still had larger and thicker bones in the lower leg than those who had never done sports.
“This result is particularly important, because we know that a bone with a large circumference is more durable and resistant to fractures than a narrower bone,” says Nilsson.
The researchers also studied bone density throughout the body in around 500 randomly selected 75-year-old men. Those who had done competitive sports three or more times a week at some point between the ages of 10 and 30 had higher bone density in several parts of the body than those who had not.
The researchers have therefore established that there is a positive link between exercise while young and bone density and size. The connection is even stronger if account is taken of the type of sports done.
“The bones respond best when you're young, and if you train and load them with your own bodyweight during these years, it has a stimulating effect on their development,” says Nilsson. “This may be important for bone strength much later in life too, so reducing the risk of brittle bones.”
The researchers fed 12 piglets a calcium-rich diet and another 12 piglets a calcium-deficient diet during the first 18 days of their lives. When the researchers examined samples of bone marrow, organs, and hind leg bone at the end of the study, they found that the piglets fed a calcium-deficient diet had compromised bone density and strength. The bone marrow tissue of these same piglets also seemed to be predisposed to become fat cells rather than osteoblasts (bone-forming cells). The presence of fewer osteoblasts during infancy may result in a reduced ability of bones to grow and repair themselves during later years.
Osteoporosis affects an estimated 10 million men and women in the United States, with about 80 percent of cases diagnosed in women. According to the National Osteoporosis Foundation, approximately 34 million additional people are believed to have low bone mass, which places them at increased risk for osteoporosis. Most people who have osteoporosis or low bone mass do not even know they have it, and the first clue is often a fracture associated with a fall or, in severe cases, simply bending over or turning around.
The lead researcher, Dr. Chad Stahl, an associate professor in the Department of Animal Science at North Carolina State University, noted that maintaining good calcium nutrition for children and adolescents is known to be important, but that this recent study “suggests that calcium nutrition of the neonate may be of greater importance to life-long bone health due to its programming effects on mesenchymal stem cells” (bone marrow tissue from which osteoblasts are formed). This idea might cause healthcare professionals “to begin thinking about osteoporosis not so much as a disease of the elderly, but instead as a pediatric disease with later onset.”