Does a late first period protect your heart later in life?
Research shows that a late first period is linked to a higher risk of heart and blood vessel disease, not to protection. That link probably runs through factors such as excess weight or high blood pressure.
A late first period does not protect the heart. The opposite appears to be true: women whose periods began at age 16 or later had a 64% greater chance of dying from heart and blood vessel disease, according to an analysis combining 29 studies and nearly 5 million women, compared with women whose periods began at age 12 to 13. A first period at age 14 to 15 was linked to a 37% higher risk. The picture was similar for stroke: a first period at age 16 or later was linked to nearly double the chance of having a stroke.
The safest point appears to be a first period at age 12 to 13. Both very early (before age twelve) and late (after age fourteen) are linked to more narrowing of the arteries in the legs. In a large group of more than 272,000 women, that extra risk was around 36 to 43%. An early first period also came with considerably more heart and blood vessel problems than average. Deviating from the 'average' in either direction carries risk, and that is the most consistent picture to emerge from the research.
But does this mean that the age of a first period itself harms the heart? That is less certain. Research that made a greater effort to separate cause and effect found that the link runs largely through well-known risk factors: excess weight, high blood pressure, and unhealthy blood fat levels. An independent direct effect was not demonstrated. Other research confirmed something similar: once body fat was taken into account, the link with blood pressure disappeared entirely.
The age of a first period is therefore probably an early signal for underlying risk factors, not a cause in itself. That makes it more of a prompt for attention than a problem to manage directly. Women who had an early or late first period, especially in combination with excess weight or high blood pressure, would be wise to monitor those risk factors with their doctor. Hormone therapy later in life appears to raise that risk further.
This answer draws on several large combined analyses, including two that bring together dozens of studies and millions of women, supplemented by large groups of people followed for years. The link between the age of a first period and heart and blood vessel disease is therefore broadly documented, but variation between studies is large and the claim that the link is causal is less firmly established. The study that used inherited genetic variants to test for causation found that the link runs largely through intermediate risk factors. That finding weakens the case for the age of a first period being a direct cause, although it is a single study. Correction for other female-specific hormonal factors was absent from many analyses.