Vitamin A deficiency is rare in well-fed countries but remains a leading cause of preventable blindness worldwide — and vitamin A is unusual among vitamins because getting too much can be just as harmful as getting too little. This fat-soluble vitamin keeps your vision sharp in dim light, supports your immune system, and helps your…
Your respiratory rate — how many breaths you take in a minute — is one of the four classic vital signs, alongside your heart rate, blood pressure, and temperature. It’s also one of the most revealing: breathing often speeds up before anything else when the body is under strain, which makes it an early warning…
Your bilirubin levels are a window onto your liver and your red blood cells. Bilirubin is a yellow-orange pigment made when old red blood cells are broken down — the same pigment that gives a healing bruise its yellow tinge. Normally your liver clears it efficiently, but when bilirubin builds up, it can turn your…
Your sodium levels say less about how much salt you eat and more about your body’s water balance. Sodium is the main electrolyte in the fluid outside your cells, and your body guards its concentration within a narrow range — because where sodium goes, water follows. A reading that’s too high or too low is…
Prolactin levels are easy to overlook, but this pituitary hormone can quietly explain a surprising range of symptoms — from irregular periods and a low sex drive to unexplained difficulty conceiving. Prolactin’s main job is to produce breast milk, so it’s naturally high during pregnancy and breastfeeding. Outside those times, though, a raised level can…
A normal body temperature isn’t the single, fixed 37°C (98.6°F) most of us grew up with. That famous figure comes from a study in the 1800s, and modern research puts the true average a little lower — and, more importantly, shows that your temperature is always on the move. It rises and falls through the…
Your white blood cell count is your immune system’s headcount — a measure of the cells that defend you against infection. Made in your bone marrow, white blood cells patrol your blood and tissues, hunting down bacteria, viruses, and other invaders. A count that’s too high or too low can be an early clue that…
Your platelet count is one of the quiet workhorses of a routine blood test, yet it reflects something vital: your blood’s ability to stop bleeding. Platelets are tiny cell fragments that rush to any injury and clump together to seal it. Too few, and you may bruise or bleed easily; too many, and your blood…
CASE FILE #02 Heart Racing for No Reason? A doctor follows the clues to a fluttering heart. Back in the Casebook — where we work one everyday health puzzle at a time, the way a doctor thinks: gather the clues, question the suspects, follow the evidence to the answer. Every case is fictional, built from…
If your fitness watch nudges you about “Zone 2” or splits your workout into coloured heart rate zones, it’s using a simple but powerful idea: the harder you work, the faster your heart beats, and different heart rates train your body in different ways. Heart rate zones turn that relationship into five bands of intensity,…