How Alcohol Depletes B Vitamins
Alcohol depletes B vitamins through two mechanisms. First, it increases urinary excretion — alcohol is a diuretic, and water-soluble vitamins including the B complex are lost in increased urine output. Second, alcohol impairs absorption: it damages the gut lining and inhibits the transport proteins that move B vitamins from the digestive tract into the bloodstream.
The result is that even if you ate a nutritious meal, a night of drinking significantly reduces your circulating B vitamin levels by morning.
Which B Vitamins Are Most Affected?
Vitamin B1 (Thiamine)
Critical for energy metabolism and nervous system function. Chronic B1 deficiency from heavy drinking causes serious neurological problems. Even acute depletion from a single night of heavy drinking contributes to fatigue and cognitive fog the next day.
Vitamin B2 (Riboflavin)
Involved in energy production and red blood cell formation. Contributes to the general fatigue and sluggishness associated with hangovers.
Vitamin B3 (Niacin)
Plays a role in DNA repair and energy metabolism. Also involved in the metabolism of acetaldehyde — the toxic intermediate produced when your liver breaks down alcohol.
Vitamin B6 (Pyridoxine)
Important for neurotransmitter synthesis and immune function. B6 is particularly important for serotonin production, which may partly explain the mood dip many people experience the day after drinking.
Why Replenishing Them Overnight Works Better
Taking B vitamins before bed means they're available through the entire overnight processing window — when your liver is actively metabolising alcohol and depleting these nutrients in real time. Taking them in the morning is too late; the depletion has already happened during the most metabolically active period.