Vitamin D has rapidly become the de rigueur nutrient for anyone exercising a keen interest in their health. I'm sure many reading this will be well versed in the vitamin D story by now. By way of synopsis, our levels of vitamin D are in crisis, with great swathes of the population experiencing dangerously low levels.
This is especially the case through the long winter months, a period when we lose our most abundant source, sunshine. The consequences of this lack of vitamin D are grim indeed, increasing the risk of bone problems such as osteoporosis, along with a plethora of other maladies such as common cancers, heart disease, diabetes, arthritis, multiple sclerosis, Alzheimer's disease, not to mention our susceptibility to infections.
As you might imagine from this rogues gallery of ailments, this has fuelled intense research over recent years, as scientists jostle to uncover more and more of vitamin D's health promise.
A study published this week in the Journal of the American Medical Association and widely reported in the media has seemingly put a dampener on the fever pitch enthusiasm for taking your vitamin D supplements this winter.
A randomised, double-blind, placebo-controlled trial of 322 healthy adults in New Zealand, found that supplementation with high doses of vitamin D had no benefit on the incidence and severity of upper respiratory tract infections - basically colds and flu . The participants in this study received either vitamin D (an initial massive dose of 200,000 IU, then another 200,000 IU a month later, then 100,000 IU monthly) or a placebo.
This has led some journalists to ignorantly proclaim that you are wasting your money if you take vitamin D supplements this winter. But before you abandon your vitamin D supplements, here are a couple of things you need to know about the study:
1. The baseline vitamin D levels of the people in this study were higher than the UK. The average vitamin D level at the start of the study was an impressive 29ng/ml. Even in the winter, the average vitamin D level of the participants only decreased to around 20ng/ml. To put this into some context, in The Health Delusion, we recommend that people aim to keep their vitamin D levels in the range of 20-32ng/ml all year round.
In short, we can confidently conclude that most of the participants in this study already had enough vitamin D. Compare this with the UK, and it's a different story, where 47% of adults don't even reach levels of 16ng/ml in the winter and spring . In short, our vitamin D status is in poor shape compared with those taking part in this study.
2. The vitamin D dosing in this study was excessive and resulted in levels of vitamin D sustained above 48ng/ml. This is way above the level that we advocate (upper limit of 32ng/ml). Elevating vitamin D levels this high confers no added benefit, and in fact there are some early warning signs in the scientific literature that sustaining vitamin D levels at these dizzy heights could actually increase the risk of health problems such as prostate cancer and pancreatic cancer [3, 4], as well as being linked with increased mortality .
When we think about vitamin D, and just like virtually every other nutrient, we need to respect the concept of what's known as the 'U-shaped' curve of benefit. What that means is that both too little and too much of a nutrient cause problems. Where you want to be is the zone in the middle, which is neither too low, nor too high, and therefore optimal.
Take a step back and there's a valuable lesson here. Taking loads more of a nutrient, if you already have enough of it, is not a terribly smart idea. But this is not the case in the UK, where our vitamin D levels are languishing perilously low, especially throughout the winter and spring months.
So whilst the jury might be out on how effective vitamin D is or isn't when it comes to seasonal colds and flu protection, be under no illusion that limping through winter in a vitamin D deficient state is likely to amplify the risk of a multitude of other serious health problems.
Vitamin D is not the panacea for all ills that many fervent vitamin D advocates extol, but it is a pillar of health that we've grossly neglected. As we've discussed in detail in The Health Delusion, adults in the UK can achieve and maintain an ideal vitamin D level (20-32ng/ml) this winter by supplementing 1,100-1,200 IU of vitamin D daily from October through to March. Don't be deterred by this recent study - the time for vitamin D supplementation in the UK is now!
 Murdoch DR et al (2012) Effect of Vitamin D3 Supplementation on Upper Respiratory Tract Infections in Healthy Adults: The VIDARIS Randomized Controlled Trial. JAMA 308(13):1333-9
 Hyppönen E, Power C (2007) Hypovitaminosis D in British adults at age 45 y: nationwide cohort study of dietary and lifestyle predictors. Am J Clin Nutr 85(3):860-8.
 Tuohimaa P et al (2004) Both high and low levels of blood vitamin D are associated with a higher prostate cancer risk: a longitudinal, nested case-control study in the Nordic countries. Int J Cancer 108(1):104-8.
 Helzlsouer KJ et al (2010) Overview of the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers. Am J Epidemiol 172(1):4-9.
 Melamed ML et al (2008) 25-hydroxyvitamin D levels and the risk of mortality in the general population. Arch Intern Med 168(15):1629-37.