What's the deal with vitamin D?
You may have heard vitamin D referred to as the "sunshine vitamin" based on the fact it can be synthesized in the skin from exposure to sunlight. What you may not know, is that there are two types of vitamin D: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Vitamin D3 is made in the human body when ultraviolet B (UVB) radiation from the sun initiates the conversion of vitamin D3 from a compound known as 7-dehydrocholesterol. The other type of vitamin D, vitamin D2, is produced in plants and mushrooms. This too occurs due to UVB exposure; however in this case, ergosterol is converted to vitamin D2.1
This means that humans can obtain their vitamin D dose via two sources: sunlight exposure and diet. D3 can be obtained via sources such as oily fish, red meat, egg yolk and liver, whereas dietary vitamin D2 can be obtained from mushrooms grown in UV light and fortified foods.
If an individual does not obtain sufficient vitamin D from either sunlight exposure or their diet, they can become vitamin D deficient. As vitamin D helps regulate the amount of calcium and phosphate in the body, deficiency can contribute to a wide range of health problems, and even mortality.
Vitamin D and mortality
Several large-scale studies and clinical trials have linked vitamin D deficiency with mortality. However, the research to date has typically focused on older populations. As older age populations typically take a vitamin D supplement, this may have impacted the results.
In a new study presented at this year's Annual Meeting of the European Association for the Study of Diabetes (EASD) in Barcelona, researchers from the Medical University of Vienna, Austria, have investigated the effects of low vitamin D levels in the blood on overall and cause-specific mortality.2
Their research has used a large study cohort that encompasses all age groups and from a population with minimal vitamin D supplementation in old age. The authors note: "Cause-specific mortalities and the impact of age on the association of vitamin D with the risk of death have not yet been reported in detail."
Not all vitamin D is equal
It is important to know that because the liver metabolizes vitamin D2 and D3 in different ways, they are not equal when it comes to raising your overall vitamin D status.
The hydroxylation of vitamin D3 by the liver enzyme cholecalciferol 25-hydroxylase produces 25-hydroxyvitamin D. Blood levels of 25-hydroxyvitamin D are taken as a clinical measurement to determine your collective vitamin D status.1 In this study, the authors used a blood level of vitamin D nmol/L – a commonly adopted cut-off value for vitamin D deficiency – as their reference value to which other levels would be compared. Low and high levels for which risk would be calculated were 10nmol/L and 90nmol/L.
Vitamin D deficiency is linked to increased risk of mortality
To conduct the study, the scientists obtained their data from the records of 78,581 patients (mean age 51.0 years, 31.5% male) that had a vitamin D measurement taken at the Department of Laboratory Medicine, General Hospital of Vienna between 1991 and 2011.
This data was then matched with the Austrian national register of deaths. The first three years of mortality following the vitamin D measurement were excluded from the analysis, and patients were followed up for up to 20 years where achievable. Median follow-up was 10.5 years.
The study found that vitamin D levels of 10nmol/L or less were associated with a two-three fold increase in risk of death. The largest impact was observed in patients aged 45 to 60 years, where there was a 2.9x increased risk.
On the other hand, levels exceeding 90nmol/L were associated with a reduction in all cause-mortality of 30-40%. Again, the largest impact was observed in the 45 to 60-year old age cohort (a 40% reduction in risk). For patients over the age of 75 years, no statistically significant associations between vitamin D levels and mortality were found.
When assessing cause-specific mortality, the researchers were surprised to find that the strongest associations of vitamin D were with causes of death other than cancer and cardiovascular disease. The differences between age groups were even more pronounced for these causes of death, and once again the largest effect was identified in patients aged 45-60 years old.
Interestingly, there was 4.4 times higher risk of death from diabetes in vitamin D deficient groups (with vitamin D levels less than or equal to 50 nmol/L) than for participants whose serum levels were >50nmol/L.
Can you have too much vitamin D?
When plotting the risk of death according to vitamin D serum level in the cohort, the researchers found that the data did not support a risk resurgence at vitamin D levels >100 nmol/L. The authors comment that this further depletes concern over the possibility of having higher vitamin D levels.
The scientists say: "Our survival data from a large cohort, covering all age groups, from a population with minimal vitamin D supplementation at old age, confirm a strong association of vitamin D deficiency (under 50 nmol/L) with increased mortality. This association is most pronounced in the younger and middle-aged groups and for causes of deaths other than cancer and cardiovascular disease, especially diabetes."
They conclude: "Our findings strengthen the rationale for widespread vitamin D supplementation to prevent premature mortality, emphasize the need for it early in life and mitigate concerns about a possible negative effect at higher levels."
1. Rathish Nair and Arun Maseeh. Vitamin D: The “sunshine” vitamin. Journal of Pharmacology and Pharmacotherapeutics. DOI: 10.4103/0976-500X.95506.
2. Marculescu, Endler, Yang and Haidinger. 2019. Vitamin D Deficiency, Overall and Cause-specific Mortality - the Impact of Age and Diabetes. Poster Presentation. This material has been peer reviewed. There is no full paper at this stage.