Researchers from the Faculty of Health and Medical Sciences at Copenhagen's University evaluated blood samples from 247,574 individuals obtained from Copenhagen's General Practitioners Laboratory. The study is the largest of its kind, and its findings support other research that has found that vitamin D is of benefit with regard to mortality risk, although the results also demonstrated that people with too high levels of vitamin D had a higher rate of mortality.
Darshana Durup, a PhD student, explained:
"Our data material covers a wide age range. The people who participated had approached their own general practitioners for a variety of reasons and had had the vitamin D level in their bloodstream measured in that context. This means that while the study can show a possible association between mortality and a high level of vitamin D, we cannot as yet explain the higher risk."
In future research, the team wants to compare their results with data obtained from disease registers like the cancer register.
Durup, continues: "We have had access to blood tests from a quarter of a million Copenhageners. We found higher mortality in people with a low level of vitamin D in their blood, but to our surprise, we also found it in people with a high level of vitamin D. We can draw a graph showing that perhaps it is harmful with too little and too much vitamin D."
Whilst the lowest mortality rate occurs in blood levels containing 50 nmol of vitamin per liter of serum, the team discovered a 2.31 higher mortality risk in those with less than 10 nanomol (nmol) of vitamin per liter of serum, and a 1.42-fold higher risk of mortality in blood levels containing over 140 nmol of vitamin per liter of serum.
Durup points out that although scientists have no knowledge about the causes for the higher mortality rate, she hypothesizes the new findings may be used to investigate claims of those who say that one can never get too much vitamin D.
"It is important to conduct further studies in order to understand the relationship. A lot of research has been conducted on the risk of vitamin D deficiency. However, there is no scientific evidence for a 'more is better' argument for vitamin D, and our study does not support the argument either. We hope that our study will inspire others to study the cause of higher mortality with a high level of vitamin D."
She concludes: "We have moved into a controversial area that stirs up strong feelings just like debates on global warming and research on nutrition. But our results are based on a quarter of a million blood tests and provide an interesting starting point for further research."
Written By Petra Rattue