Everything Under the Sun: Your Primer on Vitamin D

What is vitamin D good for? We're here to answer all your burning questions.

Man laying on a towel on a beach in the sun with a Huel shaker next to him

That burning ball of hot plasma, approximately 151,000,000 kilometers from Earth, is responsible for far more than just your glowing tan. Exposure to the sun's rays causes the body to make a vital micronutrient, vitamin D, which is loaded with biological benefits and essential for maintaining a healthy, balanced lifestyle. Every single cell in your body uses vitamin D, so getting enough of it should be near the top of your daily to-do list.

There's a strong chance, however, that you don't. More than 40 percent of US adults have a vitamin D deficiency, and as many as one in five Brits, especially during spring and winter. Thankfully, you can flip the switch on your vitamin D intake almost instantly. Below, we shine a light on the very real benefits of vitamin D, how best to get it, and the easy-to-miss signs of vitamin D deficiency.

What Does Vitamin D Do?

As we’ve already touched on, vitamin D is vital for dozens of bodily functions that keep you alive. One of the most prevalent examples—and one of the reasons Public Health England (PHE) recommends we all take it as a supplement—is that it “regulates the immune system in several ways,” explains Daniel Clarke, junior sustainable nutrition manager at Huel. “It affects T-cell activation—cells key for fighting infections—and vitamin D receptors are expressed on multiple immune cells (B cells, T cells, and antigen-presenting cells), which are all capable of making active vitamin D.”

By regulating the amount of calcium in your body, vitamin D also plays a crucial role in maintaining strong bones and teeth. For muscle mass, Clarke explains, its relationship with the sunshine vitamin isn’t so clear, especially as there’s already a significant correlation between physical activity and higher vitamin D levels. “A lot of the benefits are seen in older adults, who are at greater risk of bone fractures and a lack of physical activity,” says Clarke.

How To Get Vitamin D

The simplest (and cheapest) way of maintaining vitamin D is to spend more time in the sun. That’s because it’s a steroid hormone that’s produced by your liver and kidneys, which starts with UVB in sunlight converting cholesterol into pre-vitamin D3. You need those rays to fall directly onto your bare skin, and not through your clothes or a window.

Alternatively, vitamin D supplements – which are available in every high street health store or chemist (as well as in every serving of Huel) – are a convenient way to ensure you’re getting your intake.

Most experts advise to take at least 400–800 IU/day or 10–20 micrograms. “Choose vitamin D3 (cholecalciferol) over vitamin D2 (ergocalciferol) as it's more bioavailable," says Clarke. "As vitamin D is fat-soluble, take the supplement alongside foods that contain some fat to help increase absorption. Despite this, vitamin D deficiency remains a prevalent problem during winter, when days are shorter and direct sunlight is scarce.

Understanding Vitamin D Deficiency

It’s not only those living in colder climates that are at risk from vitamin D deficiency. It’s estimated that one billion people worldwide are grappling with it. Of that one billion, vegetarians and those following dairy-free diets are at particular risk of deficiency as their diets may be lacking necessary nutrients which are typically found in animal-based foods.

If you think you have a low vitamin D intake, there are three signs to be wary of.

First, are you experiencing regular low moods? Serotonin, your happy hormone, tanks without sun exposure.

Similarly, excessive sweating is also a sign of vitamin D deficiency, alongside weakness and confusion. People with darker skin – especially those from African, African-Caribbean, or south Asian backgrounds – are at risk of not producing enough vitamin D from sunlight. This is due to “the skin pigment melanin,” Clarke explains, “that, while reducing the harmful effects of the sun's rays, also reduces the conversion of cholesterol to pre-vitamin D3.”

How Much Vitamin D Do I Need?

Let’s end on a positive note. Just five to 30 minutes of sun exposure twice a week will keep your vit-D at an optimum level, according to the National Institutes of Health. If you’re looking to take it through a supplement, you probably don’t need as much as you think. “Often, people take high-level vitamin D supplements,” says Clarke. “800IU to 2000IU a day should be fine.”