In the news
Especially in winter we should take extra vitamin D, because then we produce less vitamin D ourselves due to a lack of sunlight. Keeping track of your vitamin D reserves is important, as a deficiency is said to cause porous bones and has also been linked to diabetes, heart disease and cancer. How is that right?
Factcheck
Most people have lower vitamin D levels towards the end of winter. This is the result of less sunlight, which is needed to produce this vitamin in our body. Because vitamin D supplements have no proven health benefit for healthy adults for now, they are not systematically recommended. In addition, there is no scientific evidence that extra vitamin D protects against diabetes, heart disease and cancer.
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Where does this news come from?
Exposure to UV light is crucial to ensure adequate vitamin D levels. By the end of winter, most adults have lower blood levels of vitamin D. The question is whether these lower values are the cause of health problems that you should treat with vitamin D supplements.
For years, vitamin D supplements have been among the most sold dietary supplements, because vitamin D is said to protect against diabetes, heart disease and cancer. It is useful to look closely at the results of one of the largest intervention studies with vitamin D, namely the VITAL study (1):
- It included 25,871 American men and women over the age of 50 who took vitamin D or a sham drug for 5 years.
- The number of cancers, cardiovascular diseases and all-cause mortality did not decrease in the vitamin D group.
- Even the number of broken bones did not decrease (2).
- In other intervention studies, researchers also found no protection against cancer (3) or against diabetes (4).
- In short, large intervention studies confirm the findings of the authors of the extensive VITAL study: the majority of the more than 200 investigated intervention studies with vitamin D yielded no results, in contrast to methodologically weaker studies that showed positive effects of vitamin D (5) .
- The explanation for this contradiction is simple: in these last weak studies, participants with healthy eating and lifestyle habits have higher vitamin D values than participants who lead an unhealthy lifestyle and therefore suffer from chronic diseases.
- This finding suggests that vitamin D protects against a variety of chronic conditions, but no causal relationship has been established.
- This effect does not play a role in intervention studies, in which confounding factors such as obesity are evenly distributed between the intervention group and the control group. And in those well-designed studies, researchers find no connection.
Bron
(1) Manson JE, Bassuk SS, Buring JE, et al. Principal results of the VITamin D and OmegA-3 TriaL (VITAL) and updated meta-analyses of relevant vitamin D trials. J Steroid Biochem Mol Biol. 2020 Apr;198:105522.
How should you interpret this news?
Vitamin D has been the subject of scientific research in the past.
- Healthy adults have lower blood vitamin D concentrations at the end of winter, but the recommendation to systematically take vitamin D supplements is not based on scientific research.
- Researchers brought together all existing research in a systematic literature review:
- No studies have examined the detection of deficiencies and administration of vitamin D supplements in healthy adults (6).
- The fact that there is no research on it is of course no proof that it doesn’t work. But before recommendations are made on a large scale, it is essential to demonstrate the health benefit based on sound scientific research.
Healthy eating and lifestyle habits, no smoking and normal weight are much more important to prevent chronic diseases than vitamin D supplements. Certain risk groups do benefit from vitamin D supplements:
- pregnant women
- elderly people in care facilities
- people with osteoporosis
- babies under 1 year old
- adults who underwent gastric bypass surgery
Conclusion
Most people have lower vitamin D levels towards the end of winter. This is the result of less sunlight, which is needed to produce this vitamin in our body. Because vitamin D supplements have no proven health benefit for healthy adults for now, they are not systematically recommended. In addition, there is no scientific evidence that extra vitamin D protects against diabetes, heart disease and cancer.