Obesity-related risk factors for impaired lung function

Weighing the strengths and limitations of our studies, we believe our results contribute to the unraveling of causal pathways between obesity and lung function impairment. The main conclusion of the first part of this thesis is that visceral fat is associated with lung function impairment in men with the metabolic syndrome. Furthermore, we conclude that in the general population there is no causal association between insulin resistance and lung function, nor an association between visceral fat and exhaled nitric oxide. In the second part of this thesis we showed that vitamin D is associated with lung function and nitric oxide in obese participants.In the study presented in this thesis antimicrobial peptides levels were lower in allergic asthmatics than in healthy controls. Unfortunately, we were not able to conclude if vitamin D supplementation influences these antimicrobial peptide levels. Larger studies are needed to investigate whether vitamin D also increases antimicrobial peptides in the lung.In summary, obesity is a global burden that influences lung function. Future research should reveal if obesity, and in particular visceral fat, causes lung inflammation and thereby impairs lung function.Large randomized trials are necessary to establish the effect of vitamin D therapy on infections in vitamin deficient patients.