Low vitamin D levels may play role in COPD progression: UK data
Low vitamin D linked to higher risk of COPD, mortality in study
Lower vitamin D levels in the blood are associated with an increased risk of chronic obstructive pulmonary disease (COPD), especially among smokers, according to a study looking at U.K. data.
Adults with COPD who had lower vitamin D levels before their diagnosis were also at an increased mortality risk than those with higher levels.
Still, more work is needed to determine whether vitamin D status is a causative factor for COPD, researchers noted.
The study, “Vitamin D status and chronic obstructive pulmonary disease risk: a prospective UK Biobank study,” was published in BMJ Open Respiratory Research.
Vitamin D deficiency associated with increased risk of inflammatory diseases
Vitamin D is a hormone and nutrient that not only is important for maintaining healthy bones, but also has anti-inflammatory, antioxidant, and neuroprotective properties.
A deficiency in vitamin D levels has been linked to an increased risk for a variety of inflammatory diseases, but reports examining its relationship with COPD have been conflicting.
Some studies have indicated that lower levels of 25-hydroxyvitamin D, or 25(OH)D — the major circulating form of vitamin D in the body — are associated with worse lung function in COPD patients. Still, not all studies have seen such an association.
Also, “although vitamin D deficiency has been associated with higher mortality in the general population, the effect on patients with COPD remains unclear,” the researchers wrote.
To examine the potential link between vitamin D levels and COPD risk and mortality, a team of researchers in China looked at data from 403,648 people without a COPD diagnosis at the time of enrollment in the UK Biobank.
The UK Biobank database contains detailed genetic and health information from more than half a million people in the U.K. who were followed for up to 15 years. Their 25(OH)D levels were measured as part of an initial blood test at study enrollment.
Whether lower concentrations of 25(OH)D are causal or contributory to COPD risk may spur future long-duration and large-scale [appropriately-controlled clinical trials].
Participants split into 5 equal groups based on their vitamin D levels
The researchers first split participants into five equal groups, or quintiles, based on their vitamin D levels. Those in the first quintile comprised the one-fifth (20%) with the lowest vitamin D levels — less than 31.7 nanomoles per liter (nmol/L) — whereas those in the fifth quintile would be the 20% with the highest levels, at or above 64.6 nmol/L.
For reference, the Endocrine Society categorizes an ideal vitamin D level as 100-150 nmol/L, and a sufficient level as being at least 75 nmol/L. On the other hand, the U.S. Institute of Medicine says 50 nmol/L is adequate for bone and overall health.
The team found that participants with higher vitamin D levels at their initial assessment had a higher socioeconomic status, ate more oily fish, and tended to use more vitamin D supplements than those with lower levels. They also were less likely to smoke or have asthma.
Over a median follow-up of 12.3 years, 11,008 cases of COPD were recorded (5,956 men and 5,052 women).
Higher blood vitamin D levels were associated with a lower risk of COPD, with the lowest risk being observed at a level of 55 nmol/L.
In final statistical analyses, the 20% of participants with the lowest vitamin D levels were found to be at a 23% higher risk of COPD than those in the fourth quintile, or the 20% with the second-highest levels (51.8-64.5 nmol/L).
The fourth quintile was used as reference because that group reflects “the typical vitamin D level in UK population,” the researchers wrote.
An even stronger association between vitamin D status and COPD risk was observed among current smokers relative to non-smokers. The relationship was also stronger in men than in women.
Among the 11,008 people who developed COPD, 2,773 died within a median of 3.8 years, 225 of which were attributed to COPD.
Low vitamin D levels linked to higher mortality risk in COPD patients
The researchers identified a link between vitamin D levels and mortality risk, where higher levels before a COPD diagnosis were associated with better survival.
In final statistical models, those in the lowest quintile of vitamin D levels had a 38% higher risk of death, and a 57% higher risk of COPD-specific death, than people in the fourth quintile.
These findings highlight an association between lower blood vitamin D levels and higher COPD risk in both smokers and never-smokers, and a higher risk of death, implying that “vitamin D might play a role in progression of COPD,” the researchers wrote.
They noted, however, that since vitamin D was only measured once at the time of enrollment in the UK Biobank, the value does not necessarily reflect a person’s long-term vitamin D status.
Nevertheless, “whether lower concentrations of 25(OH)D are causal or contributory to COPD risk may spur future long-duration and large-scale [appropriately-controlled clinical trials],” the team wrote.
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