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Vitamin A calibrates a heart clock, 24-7

Teenagers can make it seem as if hormones control the cycles of the heart. Now, scientists have proved it.

Researchers at the University of Pennsylvania in Philadelphia have shown that a molecular clock in the circulatory system oscillates in a 24-hour rhythm in step with cells in the brain. This heart cycle responds to a hormone derived from vitamin A.

Scientists have known for years about regions of the brain where cells cycle through a steady cadence of activity, called a circadian rhythm, that regulates sleep-wake cycles. The concentrations of molecules, called clock proteins, that drive this process also wax and wane over a 24-hour period.

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