No, your blood does not completely change every 7 years. While some components of blood are constantly being replaced, it's not a complete turnover within that timeframe.
Here's a breakdown:
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Red Blood Cells: These have a relatively short lifespan. The provided reference indicates that red blood cells live for only 70–120 days. This means that a significant portion of your red blood cells is replaced several times within a 7-year period.
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White Blood Cells: These cells have a longer lifespan than red blood cells. According to the reference, white blood cells live on average more than a year. So, some white blood cells will persist longer than red blood cells, but they are still replaced before 7 years.
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Other Blood Components: Plasma, the liquid portion of blood, contains various proteins, electrolytes, and other substances that are also continuously being replenished or recycled.
Therefore, while the components of your blood are constantly changing and being replaced at different rates, the idea that your entire blood supply is brand new every 7 years is a myth. Different cells within the blood have varying lifespans, all much shorter than 7 years.
