The study – published in the European Journal of Clinical Nutrition – reveals that older adults with lowvitamin D levels have a 30% greater risk of death than people who had higher levels.
Led by Ellen Smit of Oregon State University, USA, the randomised, nationally representative study found that overall, people who were frail had more than double the risk of death than those who were not frail. However, frail adults with low levels of vitamin D had triple the risk of mortality than those were not frail and who had higher levels of the sunshine vitamin.
"What this really means is that it is important to assess vitamin D levels in older adults, and especially among people who are frail," said Smit.
"Our study suggests that there is an opportunity for intervention with those who are in the pre-frail group, but could live longer, more independent lives if they get proper nutrition and exercise,” she added.
Smit noted that whilst past studies have separately associated frailty and low vitamin D with a greater mortality risk, the new study is the first to look at the combined effect.
In the study Smit and her colleagues examined more than 4,300 adults older than 60 using data from the Third National Health and Nutrition Examination Survey.
The study divided people into four groups. The low group had levels less than 50 nanograms per milliliter of vitamin D in the blood – measured as serum 25(OH)D – the highest group had vitamin D of 84 or higher.
In general, those who had lower vitamin D levels were more likely to be frail, the researchers said. However, they noted that because of the cross-sectional nature of the survey they could not determine if low vitamin D contributed to frailty, or whether frail people became vitamin D deficient because of health problems.
Smit argued however, that longitudinal analysis on death showed it may not matter which came first.
"If you have both, it may not really matter which came first because you are worse off and at greater risk of dying than other older people who are frail and who don't have low vitamin D," she said.
The authors concluded that the results of their study suggest that low serum 25(OH)D is associated with frailty, adding that there are ‘additive joint effects’ of serum 25(OH)D and frailty on all-cause mortality in older adults.
"This is an important finding because we already know there is a biological basis for this. Vitamin D impacts muscle function and bones, so it makes sense that it plays a big role in frailty," said Smit.
Source: European Journal of Clinical Nutrition
Published online ahead of print, doi:10.1038/ejcn.2012.67
“The effect of vitamin D and frailty on mortality among non-institutionalized US older adults”
Authors: E Smit, C J Crespo, Y Michael, F A Ramirez-Marrero, G R Brodowicz, S Bartlett and R E Andersen