Vitamin D is perhaps best known as the “sunshine vitamin.” Although other vitamins require a proper diet or supplementation to prevent deficiency, vitamin D is one that we can get just from going out in the sun. In the past, scientific literature associated vitamin D with bone development, but we’re investigating its contributions to cardiovascular health and immunity.
Vitamin D is essential for a healthy immune system, strong bones and teeth, and proper nerve function. We get most of our vitamin D from sunlight but find it in foods such as fatty fish, eggs, cheese, and fortified cereal. Some people may need to take vitamin D supplements to get the recommended amount. Despite its abundance, vitamin D deficiencies abound. One study estimates that as many as one billion people worldwide don’t get sufficient vitamin D.
What is vitamin D? What are its benefits? What happens when we don’t get enough of it? And how can we ensure that we do?
Vitamin D Research History
As far back as the first century AD, there have been reports of children showing signs of weak bones: bowed legs, curved spines, and frequent fractures. As a result, they’d experience muscle spasms and bone pain and sometimes develop learning disabilities as they grew older. The condition, known as rickets, resulted from vitamin D deficiency and began to spike towards the end of the 19th century when industrialisation filled the air with sun-blocking pollutants. By the turn of the 20th century, rickets led to childhood mortality rates as high as 300 out of every 1000 children in some areas.
By the early 1900s, researchers observed that certain foods helped prevent and treat rickets but believed that recently discovered vitamin A was the solution. However, English pharmacologist Edward Mellanby noted some discrepancies in that model. In experiments with dogs, for instance, Mellanby found that many of the fastest-growing animals were also those that he had given the least amount of vitamin A. Through this work, he discovered vitamin D.
In 1922, British microbiologist Dame Harriette Chick took his results and applied them to human children suffering from affliction in Vienna. She and her team demonstrated that rickets could be cured in humans through a treatment of cod liver oil and sunlight.
Her work led to effectively removing rickets from the Western world, which is why it’s virtually unheard of today. There still are cases of rickets, particularly in certain populations, but these cases are rare and treatable.
Vitamin D and Other Supplements
Vitamin D doesn’t have a direct effect on bone strength. Hardened bone depends on concentrations of phosphorus and calcium. Without vitamin D, the body only absorbs about 10 – 15% of the calcium it takes in through food and 60% of the phosphorus. With vitamin D, these numbers increase to 30-40% and 80%, respectively.
Of course, Vitamin D doesn’t just work on its own. Without magnesium, the body can’t absorb the vitamin and convert it into the prehormone that leads to the bone mineralisation process. So, for strong bones, ensure that you’re getting enough calcium and magnesium, in addition to vitamin D.
It’s worth noting that vitamin D doesn’t just promote bone hardening — a lack of it leads to bone weakening. When the body has insufficient vitamin D, it triggers a hormone response that leads to the creation of osteoclasts, which dissolve already hardened bone, resulting in increased skeletal weakening. In children and young adults, this leads to the rickets symptoms: poor or weak bone growth, bone pain, and joint swelling. In infancy and adolescence, times when the body grows the most, the need for calcium can exceed the absorption levels and lead to seizures or muscle spasms.
In adults, particularly older ones, there’s a risk of osteomalacia, which is essentially the same as rickets, but not as severe since adults are no longer growing. It can still cause bone pain, difficulty walking, and frequent fracturing. Fortunately, these conditions are generally easily treatable, as vitamin D is readily available to us.
Vitamin D and K2
Taking vitamin D and K2 together has many potential benefits for our health. These vitamins work together to support bone health, help prevent heart disease, and support cognitive function.
Vitamin D Foods
Several types of food are great sources of vitamin D, with fish generally offering the most per serving. Eating one meal with freshwater salmon could be enough to meet the daily requirement of vitamin D. Shiitake mushrooms have vitamin D in them when they’re fresh but substantially more if they’re sun-dried.
Many food manufacturers are also fortifying their products with vitamin D. Typically, these are dairy products such as milk and yoghurt, but others, such as cereals and juices, are often fortified as well.
Fresh Salmon is a good source of vitamin D
However, we receive most of our vitamin D from the sun. UVB rays from the sun will react with organic molecules beneath the skin to produce a previtamin form of D that’s converted to regular vitamin D. For people with fair skin, five to ten minutes of midday sun exposure could be enough to get a day’s worth of vitamin D. Additionally since sunlight will destroy unnecessary previtamins, it’s not possible to reach toxic levels of vitamin D from being out in the sun too long.
Unfortunately, the accumulated effect of this sunlight exposure can lead to sunburn and, over time, certain types of skin cancer. In addition, the same sunscreen that prevents UV rays from burning our skin also limits the amount of vitamin D previtamin they can produce. Fortunately, we can wear sunscreen and still receive the vitamin D that we need through diet or supplemental vitamins, as dermatologists recommend.
Vitamin D Deficiency Symptoms
Despite its abundance, as many as one billion people worldwide are vitamin D deficient. So if we can get a sufficient amount from as little as 10 minutes in the sun, and staple foods, why do so many people lack the nutrient?
In many cases, people don’t get enough sun exposure. As noted above, ten minutes of the sun could be enough to meet the daily requirement, but this applies to midday sun and only to the most fair-skinned among us. Those with darker skin or who wear sunscreen may not be getting enough.
Sun exposure is the preferred source of Vitamin D
Also, while vitamin D can be found in fish, beef liver, or fortified milk, these foods don’t necessarily have enough on their own to combat deficiency. In fact, less than 10% of our vitamin D comes from food sources. Additionally, many people avoid such food due to dietary needs or ethical concerns. Those who adhere to a vegan diet, in particular, could benefit from having a blood test to check their levels and ensure that they’re receiving adequate amounts of vitamin D.
Deficiencies could also be the result of other medical concerns. Since the body needs to convert vitamin D to different forms than what we ingest or receive from the sun, blood tests detecting insufficient vitamin D could indicate kidney or liver problems. Conditions such as Crohn’s disease or celiac disease, which impair the ability of the digestive tract to absorb nutrients, could also be the culprit.
Vitamin D in pregnancy and child development
Pregnancy and nursing may also result in low levels. For example, a study found that even among those who take a multivitamin, 73% of mothers and 80% of their newborns had suboptimal levels of vitamin D.
Breast milk typically has a low level of vitamin D. Still, lactating mothers who take vitamin D supplements of 4000 IUs per day can not only raise their vitamin D levels but also pass enough in their milk to prevent deficiencies in the infant. Since the formula is often fortified with vitamin D, bottle-fed babies shouldn’t need any additional supplementation.
Vitamin D is essential for childhood development as inadequate amounts could lead to rickets. While rickets are relatively rare, several reports indicate that the incidence rate is on the rise. It’s also important to note that these severe disorders aren’t the only risks involved with inadequate vitamin D.
In adults, insufficient vitamin D can lead to osteoporosis and fractures, particularly in older adults who reside in assisted living centres and may not receive enough sun exposure. Geographic location also plays a factor. Areas further from the equator receive less sunlight and associated UVB rays. Every 10-degree latitudinal move from the equator increased the probability of hip fracture by .6%.
There’s also evidence linking low vitamin D to other conditions unrelated to bone development. Patients suffering from end-stage renal disease lived longer when they had higher vitamin D levels in their system. Mice bred without the proper receptor for vitamin D develop hypertension. Multiple sclerosis and type 1 diabetes are both associated with vitamin D deficiency, suggesting that there may be a link between vitamin D and the immune system. These ideas are all gaining support in the scientific literature, though more research is needed.
On the fringe, there are conflicting studies linking vitamin D deficiency to depression, high cholesterol, and some forms of cancer, though the effect in any of these cases is likely small, if it exists at all.
Vitamin D2 vs D3
There are two types of vitamin D, D2 and D3. D2 originates in plant sources while D3 comes from animal sources, including us (the vitamin D we create from sunlight is of the D3 variety). They both lead to the production of the same prehormone, so there’s no functional difference between the two.
In terms of which is more effective, the question is somewhat controversial. While the majority of studies have shown D3 to be more effective in triggering the production of 25(OH)D — the chemical we look for when testing for vitamin D levels — others have concluded that both are equally effective.
The differing conclusions may stem from methodologies. The studies that found a more significant effect from D3 gave subjects fewer but more potent doses and ran blood tests weeks after the final dose. In contrast, those that found the two vitamins had similar effects studied subjects who took consistent daily supplements. This makes sense as D2 doesn’t bind as well to human receptors and doesn’t last as long in our bodies. However, as long as they’re consistently replenished, D2 and D3 perform comparably, so either is a fine choice for supplementation.
Vitamin D Side Effects
Like all vitamins, D can be dangerous in high doses; however, intoxication from vitamin D is rare. Although case studies exist, there aren’t enough examples for a statistic. An adult would need to ingest the equivalent of more than 20 vitamin D capsules per day in order to reach toxic levels. This could lead to excess calcium or phosphates in the blood, possibly resulting in severe symptoms such as kidney stones, cardiac arrest, or psychological conditions like depression or hallucinations. Taking calcium supplements alongside vitamin D could exacerbate these problems.
Studies have found possible links between vitamin D and other negative health outcomes, though these connections may have mitigating factors. Some studies have suggested that very high vitamin D levels seemed to double the risk of developing pancreatic cancer, but high vitamin D levels may be a result of extensive sun exposure, which could better account for the increased risk.
Another study found a link between vitamin D supplements and increased risk of falling and fractures in women in their 70s, though this was a self-reported study and the results could be a statistical anomaly as other studies found the exact opposite effect.
Vitamin D Supplementation
The extent to which vitamin D deficiency is prevalent in the world is somewhat controversial — there’s debate as to what even constitutes a deficiency. However, supplementation is safe and, in fact, is encouraged by dermatologists, who recommend getting your vitamin D from a supplement rather than from sun exposure.
Certain populations are at higher risk for developing a vitamin D deficiency. Infants, along with pregnant or nursing mothers, are more likely to need supplementation, even above and beyond what’s provided in a typical multivitamin. Those with darker skin don’t receive as much UVB radiation from the sun and so may not receive as much vitamin D as they need. Similarly, those living in latitudes far from the equator aren’t exposed to as much sunlight and are at risk for a deficiency.
There is a prevalence of vitamin D deficiency, and the risk of reaching toxic levels is low. Taking supplements is safe and likely helpful, especially for those who are pregnant, don’t eat foods high in vitamin D, or who have limited sun exposure. The Institute of Medicine recommends 600 IUs of vitamin D per day for adults between the age of 18 and 70 and 800 IUs for adults over 70, with an upper limit of 4000 IUs for all adults.
Summary
Low levels of vitamin D can impact childhood development and bone strength in adults. Other studies have linked the deficiency in the nutrient to cardiovascular disease and several forms of cancer. For many, sun exposure may be enough to get the vitamin D they need; however, those with darker skin or who wear sunscreen, as recommended by dermatologists, may need to supplement with a diet of fortified foods or a daily vitamin.
Under most conditions, vitamin D is safe. No foods have enough of the nutrient to induce intoxication and sunlight prevents excessive amounts of the nutrient from being created in the skin. Intoxication is possible if too many supplemental vitamins are taken consistently over a long period of time, though the dosage this would require makes it unlikely for most people. There are potential long-term risks of exceeding recommended dosages, such as pancreatic cancer, though the evidence isn’t definitive at this point in time.
The minimum recommended dosage of vitamin D for most adults is 600 IUs per day, but reports suggest that many of us aren’t getting as much as we need. If you aren’t receiving the necessary vitamin D through dietary sources or sunlight, consider taking a daily vitamin to ensure optimal bone strength and, possibly, cardiovascular health.
Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomised trials — https://www.bmj.com/content/348/bmj.g2035
Fresh Salmon is a good source of vitamin D
Sun exposure is the preferred source of Vitamin D
