Multiple phonetic studies confirm that English vowels undergo coarticulatory nasalization when they occur adjacent to nasal consonants, such as in nasal-consonant-vowel or vowel-nasal contexts.
The retrieved papers consistently describe English nasalized vowels as a result of coarticulation when vowels are adjacent to nasal consonants. Papers 2, 6, 8, 9, and 10 explicitly examine and affirm this phonetic phenomenon in English, providing strong and uncontradicted support for the claim.