Vitamin D, often called the “sunshine vitamin,” is in the spotlight for its role in everything from our mood and immune system to bone strength. But, despite its name, it’s technically more of a hormone than a vitamin—our bodies produce it when exposed to sunlight. It’s been called a vitamin for so long that most of us stick with that name, even though it might not be entirely accurate.

Why Is Vitamin D So Important?

Vitamin D plays a crucial role in many processes throughout the body. It’s not just about keeping our bones strong—it actually enters the cells and can even switch certain genes on or off, affecting up to 5% of our genes. This ability helps regulate a lot of important functions, including immune responses. That’s why it’s so critical for maintaining good health.

The Role of Magnesium in Vitamin D's Effectiveness

But there’s a bit of a twist—vitamin D doesn’t work solo. It needs a supporting act, and that’s where magnesium comes in. Magnesium helps convert vitamin D into its active form, which is the one your body can actually use. Without enough magnesium, taking vitamin D might not give you the full benefits, no matter how high the dose. Think of magnesium as the key that unlocks vitamin D’s potential.
Magnesium is also crucial for balancing calcium levels, which is especially important when vitamin D is doing its job of helping you absorb calcium. If magnesium is lacking, you might end up with calcium building up in places it shouldn’t, like your blood vessels, rather than strengthening your bones where it’s needed most. So, magnesium and vitamin D really work best as a team to keep your bones strong and your body functioning properly.

Why Is Deficiency So Common?

Vitamin D deficiency is surprisingly common, even in advanced countries like the USA, where about 40% of adults are thought to be lacking. Globally, estimates range between 14% to 59%. One reason is that it’s hard to get enough from food alone. Sure, it’s present in fatty fish, egg yolks, mushrooms, and liver, but most of us don’t eat these in large enough quantities to make a difference.
The real challenge comes from geography. Vitamin D production depends on sunlight, so those of us living further from the equator—like in the UK—struggle to get enough in autumn and winter when the days are short and the sun is weak. A study from Switzerland showed that during spring and summer, just 4 to 6 minutes in the sun with 22% of your skin exposed can produce 400 IU of vitamin D. But in winter, you’d need around 6.5 hours for the same result! This explains why supplementation becomes so important during the darker months.

How Much Do We Need?

The UK government recommends a daily intake of 400 IU to maintain bone health. The NHS and the European Food Safety Authority set the upper safe limit at 4,000 IU. Dr. Rhonda Patrick, a medical researcher, points out that the right dose can vary depending on your size, weight, and existing levels of vitamin D. Some experts argue that we can handle much higher amounts—after all, on a hot day, your skin can produce up to 20,000 IU with enough sun exposure.
But there’s a catch: you can’t overdose on vitamin D from sunlight, as the body regulates its production. Problems can arise if you take too many supplements over a long time, which can lead to too much calcium in your blood. This condition, called hypercalcaemia, can weaken bones and damage the heart and kidneys. So, if you’re considering taking more than the standard dose, it’s always a good idea to consult your doctor and possibly get your levels checked.

Who Is Most at Risk?

Some groups are particularly at risk of vitamin D deficiency. As we get older, our skin produces less of a substance called 7DHC, which is key to making vitamin D from sunlight. This makes it even harder for older adults to get enough.

People with darker skin tones also face challenges because their skin naturally blocks more sunlight, which is great for avoiding sunburn but makes vitamin D production slower. This can be a real problem in places like the UK, where sunny days aren’t exactly common. Research during the initial phase of COVID-19 highlighted that darker-skinned individuals, including many NHS doctors who were among the first to die from the virus, were more likely to have low vitamin D levels.

Vitamin D and Immunity: Lessons from COVID-19

Vitamin D’s role in supporting the immune system became a hot topic during the pandemic. Studies showed that having enough vitamin D might reduce the severity of illnesses like COVID-19 by supporting T-cells—our body’s immune warriors. In fact, we sent out a blog on Vitamin D and COVID back in January 2021, and the results discussed at that time were eerily similar to the findings being discussed today.

For those who would like to revisit that blog, here is the link.

That blog also had a link to a video by Professor Roger Seheult, an American Medical Doctor. For the more technically minded its well worth watching.

Here are some of the key facts from the 2021 blog:

• A study of 14,000 COVID positive patients in Israel showed that low Vitamin D levels doubled the risk of hospitalisation
• A USA study of 191,000 patients COVID positivity rate showed a clear inverse relationship with Vitamin D level. The higher the Vitamin D, the lower the rate. This study also looked in detail at the rate by geography, race, age and sex and found that in every case the higher the Vitamin D level, the lower the rate.
• A study of 20 European countries looked at the number of cases and mortality of patients compared to the average Vitamin D levels in each country and found an inverse relationship. i.e. the higher the Vitamin D, the lower the number of cases and the lower the mortality.
  A randomised controlled study of COVID positive patients who were given Vitamin D supplements, showed 2% went to ICU, compared to 50% from the placebo group. This study was only 76 patients and is going to be repeated with a larger population.
• A French study of nursing home patients showed that those who were given 80,000 iu per 2 to 3 months had a much higher survival rate than those who hadn’t had any Vitamin D in the previous month.

Clearly a lot of studies suggested there was a strong correlation between Vitamin D levels and acute respiratory infections (ARI). Evidence showed that COVID cases, ICU and mortality were all inversely proportional to Vitamin D levels. That meant the higher your Vitamin D level, within limits, the lower your chances of getting COVID, needing ICU and it being fatal.

Dr. David Grimes, a consultant physician, notes that vitamin D helps the immune system respond more effectively, which could mean fewer infections and better recovery when we do get ill. It’s like giving your immune system a bit of extra strength when it needs it most.
Dr. Grimes also points out that in cases of serious deficiency, a single high dose of vitamin D might be used to boost levels quickly, but it can take a week before it becomes effective. This approach isn’t common in the UK, even though it’s used in countries like Spain and Italy.

Vitamin D, Magnesium, and Long-Term Health

The benefits of vitamin D extend beyond immunity. It’s crucial for mental health, with low levels linked to mood disorders like Seasonal Affective Disorder (SAD) and depression. It also plays a role in maintaining strong bones by helping the body absorb calcium. But remember, without enough magnesium, this process doesn’t work as well, and you might not be getting all the benefits of your vitamin D.
Magnesium is like the supporting player that makes sure the calcium ends up in your bones—not where it doesn’t belong, like soft tissues. That’s why some people choose to take a magnesium supplement along with vitamin D. And of course, eating magnesium-rich foods like leafy greens, nuts, and seeds can help keep everything in balance naturally.

There’s also some research exploring potential links between low vitamin D levels and conditions like multiple sclerosis (MS). MS is more common in countries further from the equator, where vitamin D deficiencies are common, suggesting there might be a connection. However, while we know that low vitamin D can increase the risk, there’s no clear evidence yet that higher levels can prevent MS.

How Can You Boost Your Vitamin D Levels?

If you’re in a sunny place, getting outside is the easiest way to boost your vitamin D. But let’s be honest—that’s not always an option in the UK. For many, a daily supplement is the best bet, especially in the winter months. Dr. Grimes suggests that finding the right dose means testing your levels first and then adjusting your intake.
Some people also take vitamin K2 alongside vitamin D to ensure that calcium goes to the right places, like bones, rather than tissues, where it could cause problems. It’s an extra step that can make a big difference, especially for those with concerns about heart health.

So, Should You Be Taking a Vitamin D Supplement?

You simply can’t get enough from food and that’s probably why in 2016 the UK government recommended everyone should take Vitamin D supplements. Probably, as we are all living somewhere with long winters and limited sun. But as with most things, balance is key. Too little vitamin D can lead to a range of health problems, but too much can cause issues as well. And don’t forget about magnesium—without it, your vitamin D might not be doing its job properly. If you’re unsure, chat with your doctor, especially before taking high doses. And when the sun does shine, take the opportunity to soak it up responsibly—your body will thank you for it.

We will be blogging on Vitamin K2 and it’s importance to take alongside Vitamin D in a blog in the near future. If you have found this blog interesting, then the K2 blog is likely to be just as much.