The commonly cited limit is 400 mg for healthy adults, but the dose in a cup varies enormously and the timing matters as much as the total. What is in what, who should have less, and why an afternoon coffee costs you sleep.
The 21-day rule is a misquote and the research says otherwise. What makes a behaviour automatic, why the first version should be embarrassingly small, and what to do about the day you miss.
The number is less useful than the timing. Here is what the guidance says by age, why "I only need five hours" is almost always wrong, and the one habit that fixes more sleep problems than any other.
The eight-glasses rule has no clear scientific source. Here is what official guidance says, why your requirement differs from everyone else's, and how to tell if you are drinking enough.
Positions differ in four measurable ways — depth, angle, who controls the movement, and physical effort. Understanding those four explains preference better than any ranked list.
Men and women report orgasm at very different rates in heterosexual encounters. The gap nearly vanishes in other contexts, and that single fact rules out most of the popular explanations.
The right position depends on which movement triggers your pain, and the answer is opposite for the two main patterns. Generic advice helps one group and makes the other worse.
They are the most recommended and most incorrectly performed exercise in medicine. What the muscles do, what the evidence supports, and the mistakes that make months of effort useless.
Stress lowers desire, poor sleep lowers desire, and both are made worse by the anxiety that follows. The loop is well described, and it usually breaks at the sleep end first.
Most infections cause no symptoms at all, which makes "I feel fine" the least reliable reason to skip a test. What the test involves, what it does not, and how often is sensible.
Some of the claimed benefits are well supported, some rest on a single small study, and one widely repeated figure is simply wrong. A sober look at what the research does and does not establish.
Desire drops for identifiable reasons, and the most common ones are treatable. Medications, sleep, thyroid and mood account for a large share, and all four are checkable.