BACKGROUND Occasionally blood donation has a negative influence on some donors, while others express feelings of increased energy or wellbeing after donation. Some donors even report symptoms such as headache or feelings of unease indicating “it is time to donate blood again.” This study aims to determine symptoms and frequencies of blood donors experiencing positive and negative effects of blood donation, and study possible associations with sex, age, body mass index, smoking status, and hemoglobin level. STUDY DESIGN AND METHODS We developed and validated a questionnaire with eight predefined physical and psychological symptoms related to blood donation using a 5‐point Likert Scale. Participants in The Danish Blood Donor Study were asked to indicate if they experienced the present symptom prior to and/or after the donation. RESULTS A total of 6,073 donors were included. Of the donors, 61% experienced one or more effects of blood donation. Positive effects were experienced by 18% of the donors, 29% experienced negative effects, and 14% experienced both. Most notable positive effects were alleviated headache (14%), feeling lighter (14%), and less tiredness (7%). Most notable negative effects were less energy (25%), more dizziness (22%), and more tiredness (21%). Logistic regression analysis revealed that positive effects were more likely among donors with higher BMI, older donors, and smokers. Negative effects were more likely among younger donors, donors with lower BMI, and among female donors. CONCLUSION Analyses indicate that susceptibility to blood donation effects varies by BMI, sex, smoking status, and age, and therefore should be taken into consideration when informing donors about potential effects of blood donation.

Background Allergic rhinitis (AR), allergic conjunctivitis (AC), and asthma composing multiple phenotypes and improved understanding of these phenotypes and their respective risk factors are needed. Objectives The objective of this study was to define the prevalence of AR, AC, and asthma and their association with allergen‐specific immunoglobulin E (sIgE) sensitization in a large cohort of blood donors and identify risk factors. Methods From the nationwide population‐based Danish Blood Donor Study, 52,976 participants completed an electronic questionnaire including AR, AC, asthma, allergic predisposition, and childhood residence. Of these, 25,257 were additionally tested for sIgE to inhalation allergens (Phadiatop). Results The prevalence of sIgE sensitization, AR, AC, and asthma was 30%, 19%, 15%, and 9%, respectively. The youngest birth cohorts had the highest prevalence of sIgE sensitization and symptoms of asthma, AR, and AC, and for asthma, they apparently experienced symptoms at an earlier age. The sIgE sensitization was positively associated with male sex. The sIgE seroprevalence was higher in participants with both AR and AC (ARC) than in participants with either AR or AC. Allergic predisposition and sIgE sensitization increased the risk of the diseases, while farm upbringing was associated with reduced prevalence of ARC, however, only in sIgE sensitized participants. Conclusion Birth year, childhood residence, sIgE sensitization, and allergic predisposition were associated with asthma, AR, and AC prevalence. Individuals with self‐reported ARC represent a primarily sIgE‐positive phenotype, while those with either AR or AC represent more diverse phenotypes.

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