At this time of year, when the days are darker, and we spend less time outdoors, many of us risk becoming vitamin D deficient. Research shows that one billion people around the world are vitamin D deficient, a reality that has ramifications for our health (more on which later).

It is well known that sun exposure is the easiest way to stimulate the production of vitamin D in the body, which is why we’re particularly vulnerable to deficiency in the dark winter months. “The NHS recommends supplementing with vitamin D3 throughout autumn and the winter months for this reason,” explains Rhian Stephenson, nutritionist, naturopath, and founder of Artah.

Without sunlight, there are other ways of ensuring we get our vitamin D fix. “Most foods are poor sources of vitamin D, but the ones that do offer it include salmon, swordfish, tuna, full fat dairy that’s fortified with vitamin D, sardines, beef liver, cod liver oil, and egg yolks,” says Stephenson, who emphasizes that eating such foods won’t deliver adequate levels, but will help. She warns that those who eat a vegan diet are particularly at risk of vitamin D deficiency.

When it comes to supplements, which can be key to preventing deficiency, Stephenson says that recommendations vary by country. “In the U.S. and Canada, the RDA is 600IU per day for adults and 800IU per day for individuals over 70, while in the UK, the RDA is 400IU,” she says. “The bare minimum is 400IU—[but] in my experience, this is too low to correct an insufficient or deficient status.”

It’s also worth noting that supplements are available in D2 and D3 forms, but you should always opt for D3. “In addition, look for supplements that are paired with vitamin K2, like our Essential D3/K2, because they work together to optimize calcium metabolism. Without K2, calcium can accumulate and deposit in arteries rather than being transported to our bones,” she adds.

Why is vitamin D good for the body?
Optimal vitamin D levels are essential for systemic health. “It regulates cellular growth and gene expression (essential for cancer prevention), improves cell differentiation, and is involved in immunity, fertility, muscle strength, hormone balance, sexual health, energy, mood, and more,” says Stephenson. Put simply, it’s essential for all-around health and well-being.

What happens if you’re vitamin D deficient?
Vitamin D deficiency impacts both physical and mental health. We all know about osteoporosis, but low levels are also linked to poor immunity, depression, and back pain—to name three problems. “It’s linked to poor outcomes across the board—from autoimmune conditions, Covid-19, and cancer to general immunity, hormone health, and mood disorders,” says Stephenson. Hypertension, diabetes, fibromyalgia, and neurological disorders, such as multiple sclerosis, are all also linked to vitamin D deficiency.

What are the symptoms of vitamin D deficiency?
The only way to truly know if you are vitamin D deficient is to have a blood test via your general practitioner. However, there are also signs and symptoms you can look out for.

1. Fatigue
   When you have a severe vitamin D deficiency, one of the most common symptoms is a feeling of chronic, profound, or irremediable fatigue. To add to that, poor sleep is another symptom.
2. Bone and Muscle Pain
   Some studies have shown a correlation between vitamin D deficiency and frequent muscle pain and weakness. Meanwhile, bone and joint pain are common, as vitamin D is essential for the body to absorb calcium—without it, increased fragility and pain may occur.
3. Hair Loss
   It’s essential for healthy hair that grows optimally. A deficiency can cause hair to fall out or slow growth because a deficiency intervenes with a follicle’s life cycle. Alopecia is also believed to be related to vitamin D insufficiency.
4. You’re Often Sick
   Vitamin D deficiency is associated with a weak immune system. If you’re often ill and don’t know why, consider getting a blood test.
5. Depression, Anxiety, and Mood Disorders
   Scientific research shows that vitamin D may play a key role in balancing our mood and minimizing the risk of depression. Low levels can contribute to seasonal affective disorder and are often associated with feelings of overwhelm, sadness, anxiety, forgetfulness, and sadness.