Posted on 25 November 2022
Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.
Why is this research important: Vitamin D is an important nutrient, perhaps most notably for bone health and for the immune system. Older people tend to be more at risk of vitamin D insufficiency (below optimal vitamin D intake) and deficiency (a lack of vitamin D likely to result in more serious health problems). Vitamin D is manufactured in the skin when it is exposed to sunlight, and can also be obtained from the diet. Research suggests that supplements can help prevent vitamin D deficiency, especially during the winter months, and thereby prevent various health problems. However, this topic has been controversial, as not all studies agree that supplements can make a significant difference.
What did the researchers do: In this study, researchers looked at data from the Vitamin D and Omega-3 Trial (VITAL), a trial in which around 25900 participants aged 50 and over in the United States were randomly assigned to receive vitamin D3, n-3 fatty acids, both, or a placebo. Participants reported each year whether they had sustained any bone fractures, and these were verified by review of medical records. Participants were followed up for a median (a type of average) of 5.3 years. Researchers performed statistical analyses to investigate whether taking vitamin D lowered the risk of bone fractures.
Key takeaway(s) from this research: Taking vitamin D3 was associated with a 2% reduction in bone fracture incidence, which was not found to be significant – in other words, the researchers failed to find convincing evidence that vitamin D3 supplements lower bone fracture risk. This might sound discouraging, especially given that this was a ‘gold standard’ randomised, placebo-controlled trial design with a relatively large sample size. However, there are a few important caveats to consider.
About 60% of participants had circulating vitamin D levels measured at the start of the study, and only about 10% had these measurements taken at both the start and at the end of the study period. These measurements suggested that around 13% of participants were vitamin D deficient, and that supplementation increased circulating vitamin D by about 40% on average. However, we don’t actually have a full picture of how successful vitamin D administration was at correcting vitamin D deficiency across the entire population.
Participants were given 2000IU (50 microgrammes) of vitamin D per day, and researchers relied on self-reporting to assess how well this dose was adhered to. Based on this, adherence was around 85%, but was likely to be lower than this in practice as self-reporting is rather unreliable (it’s easy to forget to take a pill and not realise/remember). Bone fractures, on the other hand, are unlikely to be underestimated – if you forgot you broke your hip last month, you probably have bigger health concerns than vitamin D deficiency. Furthermore, self-reporting suggests that around 10% of people in the placebo group actually started taking vitamin D supplements of their own accord during the study.
So in summary, while these results are a little discouraging, there are quite a few ways in which the benefits of vitamin D could have been underestimated, especially when it comes to people who are vitamin D deficient, for whom the benefits of supplementation are likely to be the largest. To know whether supplementation works or not, we need to know what a person’s starting levels of vitamin D are, we need to know whether supplementation increased those levels, and then we need to know whether that person’s risk of disease was reduced relative to a similar person taking a placebo treatment.
Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults: https://www.nejm.org/doi/full/10.1056/NEJMoa2202106
VITamin D and OmegA-3 TriaL (VITAL): Fractures, Vitamin D and Genetic Markers: NCT01704859