‘Sunshine’ Vitamin D might be the number 1 newsworthy nutrient, even more as we approach winter, and the daylight hours dwindle. And we are often told we should supplement it with vitamin K for maximum effect. But what’s the real story about these 2 nutrients if we sweep away the media noise out there? Should you supplement vitamin D, why, when, and how much? Must you always supplement vitamin D with vitamin K? And if you need D & K, what are the best supplements to consider? 

Vitamin D benefits 

It’s no exaggeration to say vitamin D is one of the most important nutrients in the body, responsible for multiple health effects. It’s actually classed as a ‘pro-hormone’ and is converted to a hormone called calcitriol that enables a wide range of vital activities. Best known for helping us absorb calcium to strengthen the structure of bones and teeth, it also ensures healthy cell division, robust immune function (while also reducing excess inflammation), making key neurotransmitters, such as serotonin for mood, regulating blood glucose, and ensuring healthy muscle function. When one nutrient supports so much ‘head-to-toe’ activity, we need to ensure we have a steady supply. Also, we need to be sure we are converting it to its active form, transporting it, and making sure it activates vitamin D receptors that respond to its signal within our cells. Any issues with these steps will reduce its effectiveness.  

Where do we get vitamin D from?  

We have a neat trick provided by nature to make our own vitamin D in skin from exposure to sunlight, where UVB rays trigger conversion of a form of cholesterol to cholecalciferol (the animal form, also called ‘vitamin D3’). As plants and other animals also make their own vitamin D, we can also obtain it in the diet, with plants providing ergocalciferol (‘vitamin D2’) and animal foods, D3. The main dietary sources are oily fish, eggs, milk products, and to a lesser extent, mushrooms, and nuts. Both forms of vitamin D are converted in the liver to 25-hydroxyvitamin D (calcidiol), then in the kidneys to the active hormone 1, 25-hydroxyvitamin D (calcitriol). The balance of evidence suggests the vitamin D3 form is more bioavailable and effective, and as we can now even obtain D3 from lichen and algae, vegans don’t need to miss out. So, look for vegan vitamin D3 forms in your supplements for that reassurance it’s working optimally.  

Am I deficient in vitamin D? 

In the northern hemisphere, with lack of sunlight, and difficulty obtaining enough vitamin D from those quite narrow dietary sources, it’s not surprising deficiency is relatively common. In the latest UK National Diet and Nutrition survey, 18% of adults had vitamin D blood levels of less than 25 nmol/L. Worldwide studies estimate up to 40% fall below this level in winter. And that’s a very low bar as optimum vitamin D levels go, since experts consider they should ideally be at least 75, if not around 100 nmol/L or more for health and disease prevention. Even in sunnier climates, insufficiency can be prevalent as people use sunscreens, cover up, or change their outdoor routine. People at risk also include those with darker skin, dieting or disordered eating patterns, liver or kidney disease, babies and the elderly, vegetarians, vegans and ‘flexitarians’, people who are pregnant, overweight, with compromised fat digestion, or using weight loss medications. Vitamin D conversion to active forms may be limited by a lack of the supporting nutrients such as magnesium. Some of us even carry slight genetic variations making us less efficient converters or with less sensitive receptors. All of these people may need more vitamin D to overcome additional challenges.