Under which regulation are chronic diseases presumed to be incurred in service?

Chronic diseases are presumed to be incurred in service under the regulation specified in 38 CFR 3.309(a). This regulation establishes conditions under which certain chronic diseases manifesting within a specific time frame post-service may be deemed as service-connected. The presumptive service connection is particularly significant as it simplifies the process for veterans seeking benefits, eliminating the need to provide direct evidence of the disease's onset during service.

By recognizing these chronic diseases as presumed service-connected, the regulation aims to facilitate access to benefits for veterans who may suffer from conditions like arthritis, diabetes, and cardiovascular disease, provided these illnesses manifest to a compensable degree within the prescribed time limit after service. This is especially relevant for veterans exposed to specific risk factors during their service that may contribute to the development of these chronic conditions.

The other regulations mentioned relate to different aspects of service connection and may address various circumstances, but they do not specifically outline the presumption of chronic diseases incurred in service as clearly as 38 CFR 3.309(a) does.