Taking a refreshing sip of soda only to be interrupted by a sudden, involuntary “hic” is common. This reaction is a direct consequence of how the digestive system reacts to carbonated beverages. Soda is a frequent culprit because the rapid introduction of gas into the stomach sets off a specific chain of physiological events. Understanding this underlying reflex explains why sparkling drinks sometimes cause this temporary annoyance.
The Mechanics of a Hiccup
A hiccup, technically known as singultus, is a temporary, involuntary reflex involving the respiratory system. The event begins with a sudden, spasmodic contraction of the diaphragm, the large muscle beneath the lungs that governs breathing. This spasm causes a quick, sharp intake of air.
Immediately following this contraction, the glottis—the opening between the vocal cords—snaps shut. This rapid closure blocks the incoming air, producing the characteristic “hic” sound. This process is managed by a complex reflex arc involving the vagus and phrenic nerves, which transmit signals between the brain, diaphragm, and digestive tract.
The reflex is triggered when these nerves become irritated or stimulated. The vagus nerve extends from the brainstem to the abdomen, while the phrenic nerves travel directly to the diaphragm. Irritation along this path disrupts the diaphragm’s normal rhythm, initiating the cycle of spasm and glottis closure.
Why Carbonation Leads to Diaphragm Spasm
Carbonation is the primary driver behind soda-induced hiccups due to the physical changes it causes in the stomach. Carbonated beverages contain dissolved carbon dioxide gas, which creates the bubbles. When consumed, this gas is introduced into the stomach where it quickly comes out of solution.
The rapid accumulation of gas causes the stomach to distend, or swell, quickly. Since the stomach is positioned immediately below the diaphragm, this sudden expansion is key. The distended stomach physically presses upward, irritating the underside of the diaphragm.
This mechanical pressure stimulates the nerve endings of the phrenic and vagus nerves passing through the area. When stimulated, these nerves trigger the hiccup reflex, causing the diaphragm to contract involuntarily. Gulping soda exacerbates this effect, as rapid consumption introduces a large volume of gas instantly, intensifying the stomach distension and nerve irritation.
Stopping Hiccups and Reducing Risk
Most hiccups resolve on their own within a few minutes, but several techniques can interrupt the reflex arc for immediate relief. Holding your breath is one common method; this increases carbon dioxide levels in the bloodstream, potentially resetting nerve signals. Slowly sipping cold water is another remedy, as it can stimulate the vagus nerve and interrupt the spasm.
To reduce the risk of soda-induced hiccups, minimize the gas entering your stomach by adjusting consumption habits. Sip your drink slowly instead of gulping, allowing gas to escape gradually. You can also allow the soda to sit open for a few minutes before drinking to let some initial carbonation dissipate. Avoiding the use of a straw also helps, as straws often cause you to swallow additional air, compounding the stomach distension effect.