Serum 25-Hydroxyvitamin D Levels and Asthma in Adults
Serum 25-Hydroxyvitamin D Levels and Asthma in Adults
The impact of low vitamin D status on asthma development is unclear. The authors investigated the relation between the baseline serum 25-hydroxyvitamin D (25(OH)D) level and incident asthma in adults, including possible effect modification by allergy status, using allergic rhinitis as a proxy measure. A cohort of 25,616 Norwegian adults aged 19–55 years participated in 2 surveys of the Nord-Trøndelag Health Study known as HUNT 2 (1995–1997) and HUNT 3.(2006–2008) Of this cohort, a nested case-control study included 584 new-onset asthma cases and 1,958 nonasthma controls whose baseline serum 25(OH)D levels were measured. After adjustment for potential asthma risk factors, the baseline serum level of 25(OH)D (<50 nmol/L) was not significantly associated with asthma in either women (adjusted odds ratio = 0.94, 95% confidence interval (CI): 0.67, 1.32) or men (adjusted odds ratio = 1.47, 95% CI: 0.93, 2.32). In men, allergic rhinitis modified the association with the adjusted odds ratio being 0.87 (95% CI: 0.36, 2.06) among men with allergic rhinitis and 2.32 (95% CI: 1.06, 5.10) among men without allergic rhinitis. The serum 25(OH)D level was not associated with incident asthma in women, regardless of allergy status. Low vitamin D status was not significantly associated with incident asthma in most adults, but it may have increased risk among men without allergy.
The relation between vitamin D status and asthma development is highly controversial: Wjst and Dold claim that asthma is caused by vitamin D supplementation, while Litonjua and Weiss assert that asthma is caused by vitamin D deficiency. Previous studies of vitamin D intake have yielded conflicting results, possibly because of the studies' reliance on questionnaire data on vitamin D in diet and supplements without incorporating skin synthesis of vitamin D after sun exposure. Measurement of serum 25-hydroxyvitamin D (25(OH)D) integrates all sources of vitamin D and is the best available approach to determine the body vitamin D status.
Although high serum 25(OH)D levels were recently found to be associated with a reduced risk of asthma-related symptoms, such as wheeze, this may be explained by reduced respiratory infections alone. The impact of 25(OH)D on the development of actual asthma is unclear. To date, there are few prospective studies on serum 25(OH)D levels and incident asthma, and they have yielded mixed findings and focused primarily on children. A recent cross-sectional study observed a significant association between a lower serum 25(OH)D level and a higher risk of ever asthma diagnosis among nonatopic but not atopic individuals. In the present study, we evaluated the association between baseline serum 25(OH)D levels and incident asthma among Norwegian adults in the Nord-Trøndelag Health Study (HUNT). We also explored possible effect modification by allergy status.
Abstract and Introduction
Abstract
The impact of low vitamin D status on asthma development is unclear. The authors investigated the relation between the baseline serum 25-hydroxyvitamin D (25(OH)D) level and incident asthma in adults, including possible effect modification by allergy status, using allergic rhinitis as a proxy measure. A cohort of 25,616 Norwegian adults aged 19–55 years participated in 2 surveys of the Nord-Trøndelag Health Study known as HUNT 2 (1995–1997) and HUNT 3.(2006–2008) Of this cohort, a nested case-control study included 584 new-onset asthma cases and 1,958 nonasthma controls whose baseline serum 25(OH)D levels were measured. After adjustment for potential asthma risk factors, the baseline serum level of 25(OH)D (<50 nmol/L) was not significantly associated with asthma in either women (adjusted odds ratio = 0.94, 95% confidence interval (CI): 0.67, 1.32) or men (adjusted odds ratio = 1.47, 95% CI: 0.93, 2.32). In men, allergic rhinitis modified the association with the adjusted odds ratio being 0.87 (95% CI: 0.36, 2.06) among men with allergic rhinitis and 2.32 (95% CI: 1.06, 5.10) among men without allergic rhinitis. The serum 25(OH)D level was not associated with incident asthma in women, regardless of allergy status. Low vitamin D status was not significantly associated with incident asthma in most adults, but it may have increased risk among men without allergy.
Introduction
The relation between vitamin D status and asthma development is highly controversial: Wjst and Dold claim that asthma is caused by vitamin D supplementation, while Litonjua and Weiss assert that asthma is caused by vitamin D deficiency. Previous studies of vitamin D intake have yielded conflicting results, possibly because of the studies' reliance on questionnaire data on vitamin D in diet and supplements without incorporating skin synthesis of vitamin D after sun exposure. Measurement of serum 25-hydroxyvitamin D (25(OH)D) integrates all sources of vitamin D and is the best available approach to determine the body vitamin D status.
Although high serum 25(OH)D levels were recently found to be associated with a reduced risk of asthma-related symptoms, such as wheeze, this may be explained by reduced respiratory infections alone. The impact of 25(OH)D on the development of actual asthma is unclear. To date, there are few prospective studies on serum 25(OH)D levels and incident asthma, and they have yielded mixed findings and focused primarily on children. A recent cross-sectional study observed a significant association between a lower serum 25(OH)D level and a higher risk of ever asthma diagnosis among nonatopic but not atopic individuals. In the present study, we evaluated the association between baseline serum 25(OH)D levels and incident asthma among Norwegian adults in the Nord-Trøndelag Health Study (HUNT). We also explored possible effect modification by allergy status.
