Excessive sugar consumption leads to seriously harmful conditions, such as diabetes or obesity. Being an obese person is a threat to your immunity, and it raises the risk of becoming sick. According to the study from 2017, obesity cause decreased immune response for the flu vaccine.
Despite being vaccinated, patients with obesity were twice as likely to suffer the flu than the people with normal weight. With that in mind, cessation or limitation of sugar consumption may be a serious aspect that would result in increased strength of the immune system.