The role of vitamin D in good health is complex and even contentious, but the core message is simple and unchanged: make sure you avoid deficiency.
While researchers continue to explore the pros and cons of high levels of vitamin D, there is a renewed focus on fully understanding the implications and causes of low levels.
“High doses may be beneficial but the evidence is not there,” says Professor Elina Hypponen. “The evidence is very clear, however, that vitamin D is a physiological substance that you need and you can’t be deficient otherwise your system starts breaking up in various ways.”
Alongside known influences on bone health, “breaking up” might include infections, high blood pressure, diabetes, or even increased mortality risk.
Professor Hypponen (left) has been at the forefront of this research for nearly two decades, in her native Finland, for 12 years at University College London, and now with the Sansom Institute, where she is Professor of Nutritional and Genetic Epidemiology.
She has authored more than 100 high-profile refereed papers on the short- and long-term health effects of vitamin D and other nutritional factors and more broadly on genetic and environmental influences on growth and disease risk.
A particular focus has been on the value of vitamin D supplementation in reducing the risk of type 1 diabetes and other immunological diseases.
She also leads a large international consortium that last year showed that obesity can lead to vitamin D deficiency.
This was an important breakthrough. The link between the two was already known, but not which caused which. There had, until then, been some suggestion that a lack of vitamin D might contribute to obesity.
However, her more recent research did show there is a genetic link between low vitamin D levels and high blood pressure, suggesting vitamin D may reduce the risk of hypertension.
“Our work is based on using genetic variations to reflect differences in nutritional status or dietary intake, when we can avoid some of the methodological problems and provide more reliable evidence for true causal effects on health,” she said.
So how much vitamin D do you need to avoid being “deficient”? The US Institute of Medicine concluded, after a comprehensive review, that 600 international units a day is about right to prevent deficiency without the potential risk of causing harm, and Professor Hypponen suggests that is likely to be “spot on”, based on current evidence.
Her own research is now looking more broadly at genetic influences across the human genome and how they interact with what we do in our diet.
“I am planning to continue work combining genetic information with nutritional information to see if we can work towards more personalised nutritional guidance because there are known genetic effects in how people respond to differences in diet,” she said.
“An example is the link between salt intake and higher blood pressure which we know has a genetic background but we don’t know which genes are underlying that sensitivity.”