Niacin is a B vitamin that plays a crucial role in energy production, DNA repair, and cell signaling. Alcohol consumption can affect the absorption and metabolism of niacin. However, the exact amount of alcohol that inhibits niacin absorption is not specified in the provided sources.

According to the Office of Dietary Supplements (ODS) [2], excessive alcohol consumption can lead to niacin deficiency by decreasing its absorption, increasing its excretion, and impairing its conversion to its active form. Chronic alcoholics are at a higher risk of developing niacin deficiency and its associated health problems, such as pellagra.

The National Institute on Alcohol Abuse and Alcoholism (NIAAA) [3] reports that alcohol can interfere with the absorption of nutrients, including niacin, by damaging the lining of the digestive tract and reducing the secretion of digestive enzymes. Alcohol can also increase the excretion of niacin through the urine, leading to a decrease in its body stores.

Drug Patent Watch [1] mentions that alcohol can interact with certain medications that contain niacin, such as Niaspan, which is used to treat high cholesterol. The combination of alcohol and Niaspan can increase the risk of liver damage and flushing, a common side effect of niacin.

In conclusion, while the provided sources suggest that alcohol consumption can interfere with niacin absorption and metabolism, they do not provide a specific amount of alcohol that inhibits niacin absorption. However, it is clear that excessive alcohol consumption can lead to niacin deficiency and its associated health problems. It is recommended to limit alcohol intake and maintain a balanced diet to ensure adequate niacin intake.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ALCOHOL
[2] https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/
[3] https://pubs.niaaa.nih.gov/publications/aa22.htm