Aging and Brain Research

For years, we’ve been told that adults need eight hours of sleep every night. But where did that number come from - and is eight really the magic number? The “eight hours” idea has roots in the 19th century, when the slogan of eight hours for work, eight for recreation, and eight for sleep became popular. Today, however, researchers are taking a closer look at how humans sleep without modern conveniences such as electric lights, alarm clocks, and late-night screens. Studies of some contemporary hunter-gatherer communities have found surprisingly short periods of measured nighttime sleep—roughly 5.7 to 7.1 hours in one set of observations. People often woke naturally around dawn and did not necessarily compensate with long daytime naps. This raises an interesting question: perhaps the timing and quality of sleep matter as much as the number of hours. But there’s an important caveat. These communities cannot simply be treated as a model for modern life. Their environments, daily activ...

Knuckle cracking is a common habit, but despite longstanding warnings, there is little evidence that it causes arthritis. One unusual experiment involved Donald Unger, who cracked the knuckles of one hand for about 50 years while leaving the other hand alone. When he eventually examined both hands, neither showed signs of arthritis. Larger studies have also found no meaningful connection between knuckle cracking and osteoarthritis. The familiar popping sound comes from changes inside the joint. Knuckles contain synovial fluid, which lubricates the joint. When you stretch or pull the joint, its space briefly expands, causing gases dissolved in the fluid to form bubbles. The resulting sound can be surprisingly loud, but the process itself is considered a normal part of joint movement. For most people, cracking their knuckles gently is harmless. Research has also failed to support claims that it causes permanently swollen knuckles, loose tendons, or weaker grip strength. However, forcing ...