Niacin, also known as vitamin B3, is an essential nutrient that plays a crucial role in the body's metabolism. It is found in a variety of foods, including meat, fish, and grains, and can also be obtained through supplements. However, excessive alcohol consumption can interfere with niacin absorption, leading to deficiency and related health problems.

According to the Office of Dietary Supplements at the National Institutes of Health [2], alcohol can interfere with the body's ability to absorb and utilize niacin. Chronic alcohol consumption can lead to a deficiency in niacin, which can cause a condition called pellagra. Pellagra is characterized by skin rash, diarrhea, and mental confusion. Pellagra was once common in the United States, particularly in the South, among people who subsisted mainly on corn-based diets and heavy alcohol consumption.

The Harvard School of Public Health [3] states that heavy alcohol consumption can interfere with niacin absorption by reducing the amount of niacin that is absorbed by the small intestine. The amount of niacin that is absorbed by the body is also influenced by the amount of food in the stomach, the presence of other nutrients, and the individual's overall health status.

Drug Patent Watch [1] indicates that there is no specific safe level of alcohol for niacin absorption. The best way to ensure adequate niacin intake is to consume a balanced diet that includes niacin-rich foods and/or to take a niacin supplement as recommended by a healthcare provider.

In conclusion, excessive alcohol consumption can interfere with niacin absorption, leading to deficiency and related health problems. There is no specific safe level of alcohol for niacin absorption. To ensure adequate niacin intake, it is recommended to consume a balanced diet that includes niacin-rich foods and/or to take a niacin supplement as recommended by a healthcare provider.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ALCOHOL
[2] https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/
[3] https://www.hsph.harvard.edu/nutritionsource/niacin-vitamin-b3/