Investigating causality in the association between vitamin D status and self-reported tiredness, 2019, Havdahl et al

Andy

Andy

Retired committee member
All of authors are from University of Bristol and include Crawley's mate, George Davey Smith. ME gets mentioned a number of times.
Abstract

Self-reported tiredness or low energy, often referred to as fatigue, has been linked to low levels of circulating 25-hydroxyvitamin D (25OHD), a biomarker of vitamin D status. Although it is uncertain if the association is causal, fatigue is a common indication for testing, and correcting, low 25OHD-levels. We used two-sample Mendelian randomization to test for genetic evidence of a causal association between low 25OHD-levels and fatigue. Genetic-25OHD associations were estimated from the largest genome-wide association study of vitamin D to date, and genetic-fatigue associations were estimated in 327,478 individuals of European descent in UK Biobank, of whom 19,526 (5.96%) reported fatigue (tiredness or low energy nearly every day over the past two weeks). Using seven genome-wide significant 25OHD-reducing genetic variants, there was little evidence for a causal effect of 25OHD on fatigue (odds ratio for fatigue was 1.05 with 95% confidence interval of 0.87–1.27 per 1-SD decrease in log-transformed 25OHD). There was also little evidence of association between any individual 25OHD-reducing variant and fatigue. Our results suggest that a clinically relevant protective effect of 25OHD-levels on fatigue is unlikely. Therefore, vitamin D supplementation of the general population to raise 25OHD-levels is not likely to be useful in preventing fatigue.
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Open access at https://www.nature.com/articles/s41598-019-39359-z

Starting to build a narrative that our fatigue isn't anything out of the ordinary?
Of 15,283 individuals aged 18–45 years who were registered with general practices in England, 37.9% scored above the cutoff for substantial current fatigue on the widely used self-rated Chalder fatigue questionnaire2. A systematic review of case definitions for CFS/ME showed that cross-sectional prevalence ranged from less than 0.1% to 7.6%, depending on the criteria for duration and associated symptoms7. Findings suggest that self-reported fatigue is continuously distributed in the general population2,8,9, ranging from mild tiredness or low energy to debilitating exhaustion or weakness. Therefore, any boundary between normal and abnormal levels of fatigue may be arbitrary. Nevertheless, a threshold that has been used to classify clinically significant fatigue is self-reported tiredness or lack of energy on nearly every day or more over a period of at least two weeks10. Findings suggest that in the general population approximately 6% meet this criterion for current fatigue (feeling tired nearly all the time for more than two weeks during a one-month period)11.
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His history with Crawley/PACE means that I don't trust Davey-Smith to do any work in this area, but that abstract looked okay aside from the Chalder fatigue scale, which is probably what was just included with the data.

I hadn't seen people claiming that low vitamin D was a common cause of fatigue though, and any recommendations I'd seen about vitamin D and CFS were about the danger of CFS leading to low vitamin D when people are largely housebound.
 
I seem to recall, about 10 or so years ago, a map was put out there that compared MS and Vitamin D deficiency prevalence throughout the world with CFS and Vitamin D deficiency prevalence.

That was a long time ago, so perhaps I am mis-remembering.

If they are beginning to promote the idea that ME/CFS symptoms, piecemeal and irrespective of severity, are "normally" distributed throughout the population, I'd observe they are not the first to this dance (albeit with a different disease); it is concerning nonetheless.
 
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