There’s been a ton of hype about vitamin D in recent years. Supporters say it’s a cure-all—boosting everything from your heart health to your lifespan. But is it really the magic bullet we’ve been sold?
A top scientific group just flipped the script on what we thought we knew. So, what went wrong? We’ll break down the latest research, flag some key cautions, and unpack the new recommendations for vitamin D supplements.
Table of Contents
The Hype
Vitamin D was discovered in the early 1900s by researchers working out how to cure rickets. This was a common bone disease seen in children. They found that vitamin D plays an essential role in forming and maintaining healthy bones.
But gradually, our understanding of vitamin D’s role grew. It isn’t just important for bone health. It’s also a key regulator of processes related to immune function, muscles, cell growth, and how we process glucose. Most tissues in the body react to vitamin D in some way.
And this naturally led to an interest in seeing how vitamin D might be related to diseases beyond just rickets. Once we started looking, we found associations everywhere. The early evidence appeared in observational studies. This kind of study involves watching people in the real world to see how particular metrics — like blood levels of vitamin D — correlate with health outcomes. The results showed an association between low vitamin D and cancer, infectious diseases, autoimmune conditions, diabetes, and heart disease [1].
What’s more, researchers were sounding the alarm that a huge number of people were deficient in this key vitamin. An article in 2006 summed up the evidence. More than a third of healthy young adults had low vitamin D levels. For those seeking medical care, the number jumps to 57% [2].
A much more recent study claims around 40% of Europeans are deficient [3].
What’s going on here? Why so much deficiency? Well, there’s a simple narrative that makes sense of the data. Vitamin D deficiency is a problem of the modern world. When we used to work out in the fields all day, it wasn’t an issue. That’s because our bodies create vitamin D when our skin is exposed to sunlight. But now that we spend most of our time indoors, vitamin D levels suffer [4].
The issue seemed serious enough that some even used the word “pandemic” to describe the problem of vitamin D deficiency [5]. One group of experts commented on the problem in 2016. They wrote that vitamin D deficiency in Europe was concerning. They called for action [6].
In that context, a prestigious international organization, the Endocrine Society, published guidelines around vitamin D. Those guidelines included three important points.
First, they established optimal levels for vitamin D in the blood. They defined deficiency as below 20 ng/mL. Insufficiency, which is a milder lack, was defined as below 30 [7].
Second, they made a suggestion about supplementation. Adults up to 50 years of age should generally get at least 600 international units of vitamin D a day. Above 70, they counsel upping that to 800. But they note that more might be helpful. To hit a target of 30 ng/mL, which gets us solidly outside the insufficiency range, adults might need up to 2,000 international units of vitamin D a day [8].
Finally, they advocate for more testing of vitamin D levels. So who should be tested? They suggest we examine those who are “at risk for deficiency” [9]. And that makes total sense. But who is at risk? That turns out to be a big group. They note somewhere between 20 and 100% of the elderly are likely vitamin D deficient. Children are also at high risk. So are young and middle-aged adults [9]. So the at-risk population includes just about all of us. In fairness, the guidelines specifically call for screening in a much narrower range of cases. But the logic of their position implies a potential benefit for fairly broad testing.
Those recommendations — and others like them — have had a profound impact. An assessment in the U.S. found vitamin D supplement use jumped from 5% to 19% between 1999 and 2012, while overall use of supplements remained stable [10]. That trend continues, with the global vitamin D market projected to reach one and a half billion by 2034 [11].
Back to Earth
There’s just one problem. Much of this popular picture about vitamin D now looks wrong. The Endocrine Society itself has made some major revisions. Let me explain what happened.
First, let’s talk about that correlation between low vitamin D and health problems like cancer. The initial thought was that vitamin D was playing a causal role here. So that would mean supplementing with vitamin D could help avoid these problems.
But this raises a key issue with observational studies. Correlation isn’t the same thing as causation. Everyone knows gray hair is associated with getting older. But that doesn’t mean gray hair causes aging. And we’re not going to stay youthful if we start dying our hair.
So here’s the issue with vitamin D. Does deficiency cause ill health? Or does it merely correlate with it? For example, older adults who live in rest homes spend the majority of their time inside. As a result, they will have low vitamin D. On the other hand, healthier older adults who don’t need to be in a rest home spend more time outside. Their vitamin D levels will be higher. In this scenario, low vitamin D levels will correlate with poor health, but they clearly aren’t causing it.
This is why we always need to test ideas generated by observational studies with controlled trials. And that’s exactly what researchers have been doing with vitamin D. So what have they discovered?
One area of investigation has been heart health. The large VITAL trial looked at the effects of daily vitamin D supplementation over 5 years in a group of 25,000 older adults. During follow-up, they recorded how many heart attacks there were. Their conclusion? Vitamin D supplements didn’t reduce the rate of heart attacks. They also didn’t bring down cancer rates [12].
A study published just this month backs up this finding about cancer. It was based on a trial of over 20,000 adults who took vitamin D supplements for up to 5 years. Researchers found the cancer rates for the vitamin D group were the same as in the control [13].
Then there’s mental health. Some research has linked low vitamin D with mood disorders and cognitive decline. Depression has been a particular area of focus. The results here are mixed. On the one hand, a meta-analysis found vitamin D supplements improved symptoms for those with clinical indicators of depression [14]. But it didn’t help improve mood for those without clinically significant symptoms [15]. And this raised an interesting question: Could taking vitamin D supplements prevent depression in the first place? A large study a few years later set out to answer this question. They looked at about 18,000 older adults and monitored their mood over 5 years. They discovered the risk of developing clinically relevant depressive symptoms wasn’t lower for those taking vitamin D. And it didn’t improve their mood [16].
Let’s look finally at all-cause mortality. This gives us a broad measure of the impact of vitamin D supplements on health. A large Cochrane review of 56 trials in 2014 gave us reason for initial excitement. It found a small but statistically significant decrease in all-cause mortality with vitamin D supplementation. The risk of death was about 3% lower [17]. But more recent evidence from large-scale trials paints a different picture. A meta-analysis completed in 2020 found vitamin D supplementation made no difference when it comes to all-cause mortality [18].
These studies, and others like them, cast serious doubt on the idea that we all need to be supplementing with large doses of vitamin D to improve our health. They also cast doubt on the idea that there’s a pandemic of deficiency. But we’ll return to that in a moment.
So a population-wide rush to supplement is wrong-headed. But there are specific groups where vitamin D supplements can help. These are reflected in the new guidelines from the Endocrine Society [19].
The first group is kids. The main concern here is rickets. But there’s also evidence adequate vitamin D levels can help ward off respiratory infections. Kids up to 18 should get about 1,500 IU daily [20]. Rickets might seem like a disease from the past — something we associate with Victorian-era London. But it’s still very much a concern, especially in areas where kids don’t get enough sunlight or have diets low in vitamin D. And when it comes to respiratory infections, vitamin D is thought to play a role in our immune response.
The second group is an extremely important one. Supplementation during pregnancy can lower the risk of preeclampsia and preterm birth. It can even improve newborn health. We’re talking doses around 3,000 IU daily [21]. Pregnancy is a time when the body is under extra stress, and ensuring enough vitamin D can help with a variety of issues.
The third group is those with a high risk of progressing to diabetes. Vitamin D could play a preventative role. Studies suggest an average dose of about 3,500 IU daily [22]. Prediabetes is a condition where blood sugar levels are higher than normal but not yet high enough to be classified as diabetes. Adding vitamin D supplementation might give some extra help in delaying or preventing the progression to full-blown diabetes.
And the fourth group is adults 75 years and older. As we age, the risk of death appears to decrease with vitamin D supplementation [23]. Our skin becomes less efficient at producing vitamin D from sunlight, and our kidneys—which play a role in converting vitamin D to its active form—also slow down. This is why the guidelines specifically call out older adults as a group that benefits from regular vitamin D supplementation.
But what about those of us not in these four groups? Shouldn’t we be aiming for optimal levels of vitamin D, too? Here’s where we see one of the most significant revisions from the Endocrine Society’s earlier guidelines. In their updated recommendations, they acknowledge we have a big problem: we don’t actually know what optimal levels of vitamin D are [24]. And this led them to abandon the earlier thresholds they set for insufficiency and deficiency [25]. They also advise against routine screening for vitamin D levels [26].
If we follow the logic here, this leads us to a really important question. How do we know there is a pandemic of low vitamin D levels in the population? Well, without an agreement about an adequate level, we don’t.
But if we think about all the study evidence we’ve looked at, we can draw a tentative conclusion. We know from the studies on depression, all-cause mortality, and rickets, that people who are low in vitamin D definitely get a benefit from supplementing. At the same time, the studies that looked at vitamin D supplementation in the general population haven’t found benefits. Those two pieces of evidence together suggest most people have adequate levels of vitamin D.
It’s like sleep. If you’re already getting enough, getting a bit more isn’t likely to make you feel more rested. But if you’re sleep-deprived, some extra sleep can have a big impact on how you’re feeling. Similarly, people who are vitamin D deficient show clear benefits from supplementation, while those with adequate levels don’t gain additional advantages. That would explain why general population studies don’t show broad benefits.
Of course we can’t be certain here. But we can say that, at this point, the evidence we have doesn’t support the idea that a huge portion of the population is suffering from low levels of vitamin D.
In fact, evidence points to potential risks in the opposite direction. Especially with the recent enthusiasm for vitamin D supplements, there’s a chance we can get too much.
A 3-year clinical trial in Canada tested the impact of several daily doses of vitamin D. One group took 400 IU, another 4,000, and a third 10,000. Researchers were looking specifically at how this affected bone density. What they found was shocking. Those higher doses didn’t improve outcomes. In fact, they made things worse. Bone density in the wrist decreased by about 2.4% in the 4,000 IU group and 3.5% in the 10,000 IU group [27]. This is related to a known risk with excessive vitamin D: hypercalcemia. It can start to pull calcium from our bones, which that trial demonstrates.
Emerging evidence shows there are some additional risks with older adults we need to be aware of. Too high a dose of vitamin D may actually weaken muscles. In one study of women with low vitamin D, the intervention group took 2,800 IU of vitamin D daily for 3 months. In the end, their handgrip strength fell by 9% and their leg strength by 13% [28]. It can also increase the risk of falls. One key study focused on women and divided them into groups at different levels of daily supplementation, ranging from 400 IU to 4,800 IU, plus a placebo group. Vitamin D seemed to help, but very high doses didn’t. Those getting 1,600 and 3,200 IU daily fell the least [29]. But when it came to women with a previous history of falls, the high doses actually increased their rate of falls [30]. Another study found a similar result, with the highest doses of vitamin D associated with an increased risk of falls [31].
Current Recommendations
So when it comes to vitamin D supplementation, more is definitely not always better. Where does that leave us now? Should we be taking it?
I already talked about four particular groups and recommended doses. So what about the rest of us? The latest Endocrine Society guidelines suggest following the recommended daily intake—600 IU for younger adults, increasing to 800 IU as you hit 50 and above [32]. That dose is less than the previous Endocrine Society guideline we noted earlier. After a further 13 years of data collection and human trials, the Endocrine Society is recommending less Vitamin D compared to their previous guideline. All of this is very different from what you’ll hear from health influencers, who promote supplementing with much higher doses, often without any testing or clear indication of deficiency.
But according to the best data we currently have, this is where we are. The 600–800 IU dose for the general population ensures people aren’t deficient in vitamin D and locks in the known benefits. That’s why I reduced the dose of vitamin D in MicroVitamin from 2,000 to 1,000 IU. And just because I take a supplement, this doesn’t mean you have to, too.
Reference List
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Note: This article is for informational purposes and does not constitute medical advice. Always consult a qualified healthcare provider before making changes to your supplement routine.
