IT’S common knowledge that 15 to 20 minutes in the sun can give you a sufficient amount of vitamin D for the day. But what if you’re not able to be in the sun? How do you know if you’re experiencing a vitamin D deficiency?

Vitamin D not only helps with your metabolism and immunity, but also with your overall mood and body function. However, because signs of a vitamin D deficiency can be subtle, it can be hard to determine if you’re experiencing a lack of it.

Nicole Avena, assistant professor of Neuroscience at Mount Sinai School of Medicine, offers some advice.

“Vitamin D is produced by skin cells when they are exposed to light, this makes it unique among other vitamins which usually need to be ingested,” says Avena. “While the sun is typically the best source for vitamin D, it isn’t always easy to be in the sun due to UV exposures and also due to limited daylight in certain parts of the world, like in the northern climates. The body’s ability to produce and absorb vitamin D decreases significantly in older people compared to younger ones. ” Here are a few of the signs that you’ll need to step into the sun or eat more foods rich in vitamin D.

1. You’ll experience bone pain and feel weak. “Vitamin D regulates the metabolism of calcium and phosphate and is important in maintaining strong, hard bones,” says Avena. This means that when there’s a vitamin D deficiency, there can be issues with overall bone health and can result in bone or even joint pain. A study by the Western Journal of Medicine that muscle weakness is another sign that someone isn’t getting enough vitamin D.

2. You’ll feel tired and lethargic.

Avena points out feeling tired and even lethargic can be a sign of a vitamin D deficiency. One study published by the North American Journal of Medical Sciences took a closer look at this claim and did find that 77.2 percent of patients with low vitamin D deficiency were presented with fatigue.

3. You’re feeling moody.

Studies do show there is an interesting tie between vitamin D deficiency and depression. If you are feeling moody and don’t have an explanation for it, evaluating your vitamin D intake might be a helpful next step.

4. You’re having muscle cramps.

“You can get vitamin D from some foods,” says Avena. “Many oily fish like mackerel and herring contain vitamin D, as does egg yolk. Some dairy products are also fortified with vitamin D.(SD-Agencies)