Alcohol inhibits the brains production of ADH. ADH is antidiuretic hormone. When the brain secretes ADH the kidneys retain more water and the urine becomes more concentrated, but the blood becomes more diluted so the sodium concentration is reduced. So when you drink a beer the opposite occurs. The alcohol inhibits ADH, so the kidneys spill more water so the volume of the urine goes up while the concentration of the urine goes down. So after you drink you pee a lot of dilute urine. The consequence of this is that the blood becomes more concentrated and the sodium concentration in the body goes up. So, beer makes the sodium concentration in the body go up.
