Getting your ideal dose of daily vitamins is a tricky business. We get certain nutrients from our diets, from the sun, and from supplements, but it's still sometimes difficult to tell if we're getting what our body needs.

Vitamin D is one of the most crucial vitamins we ingest, mainly because
it actually functions like a hormone; every single cell in your body has a receptor for it.

The vitamin is found in certain foods, like fatty fish and some dairy products, but it's very difficult to get the recommended daily intake from diet alone. How much fish and dairy products could you possibly eat in one day, after all?

It's suggested that you incorporate around 400-800 IUs of vitamin D a day, but many experts say you should get even more than that.

If you're thinking that seems difficult to accomplish, you would be right.

That being said, it probably makes sense that vitamin D deficiency is very common; about 1 billion people worldwide have low levels of the vitamin, which can reveal itself in a few tell-tale ways.

Here are the signs to look out for that could mean you are vitamin D deficient.

1. Getting Sick Often

One important role that vitamin D plays is keeping your immune system strong. So, if you notice yourself getting sick often, it could be because you're lacking this nutrient.

Studies have shown that a vitamin D deficency is most commonly linked to the flu or respiratory tract infections like colds, bronchitis and pneumonia. If you notice you're often coming down with those diseases in particular, it could definitely be connected to a lack of vitamin D.

2. Chronic Fatigue

Feeling tired can have many causes -- including a vitamin D deficiency. Unfortunately, this is often overlooked as a potential cause.

If you're noticing you're constantly feeling run down, do not ignore it! Studies have shown that very low levels of vitamin D can cause severe fatigue, which can negaively impact your quality of life.

Heathline describes the results of one case study:

In one case, a woman who complained of chronic daytime fatigue and headaches was found to have a blood level of only 5.9 ng/ml. This is extremely low, as anything under 20 ng/ml is considered to be deficient.

When the woman took a vitamin D supplement, her level increased to 39 ng/ml and her symptoms resolved.

Increased vitamin D in the diet has been proven to boost mood, increase energy, and enhance daily productivity.

3. Back Pain

That's right, your achy back might be caused by a lack of vitamin D. The nutrient in question is involved in maintaining bone health through a number of mechanisms, such as improving your body's absorption of calcium.

Researchers have found that those with a deficiency were more likely to have back pain, including back pain so severe that it limits their daily activities.

Furthermore, people with vitamin D deficiency were nearly twice as likely to experience additional bone pain in their legs, ribs, or joints.

4. Hair Loss

Vitamin D has been linked to healthy hair growth -- but on the other side of the spectrum, lack of the vitamin has been linked to premature hair loss, especially in women.

If you've been noticing a rapid loss of hair (perhaps when brushing or showering) or a thin up top, you might want to increase your vitamin D intake.

5. Muscle Pain

Muscle pan is common and often difficult to pinpoint, but there is a pretty clear link between chronic pain and a vitamin D deficiency. In fact, studies have found that 71% of people with constant muscle pain were lacking this key nutrient.

The vitamin D receptor is present in nerve cells called nociceptors, which sense pain. The less vitamin D you have in your system, the more sensitive your nociceptors are, meaning the more pain you'll experience on a daily basis.

If some of these symptoms apply to you, a vitamin D deficiency may be the answer you've been looking for. It's important that you speak to your doctor and get your blood levels measured.

Luckily, this kind of deficiency is usually an easy fix. You can either increase your sun exposure (safely, of course!), eat more vitamin D rich foods, or simply take a supplement to make sure your nutrient levels are where they should be.

Image credit: Pixabay