(Read the full article on the article about belly fat .) According to the article cited, if a woman's waist is greater than 35 inches (40 inches for a man) are deemed to be at high risk for weight-related illness. The study focuses on the increasing risk as people age. My guess is that this increase in waist circumference is at least partly due to not using those abdominal muscles as much as younger people might.
So here's a reminder to engage your abdomen. You can use those muscles while climbing stairs, jogging and even just by using proper posture.