Anyone remember those old-school commercials about milk “doing a body good”? Sure, they may have been funded by the people impacted most by declining milk sales, but they weren’t total baloney. Those catchy ads (and your mom) had a legitimate argument for pushing glasses of milk on you: It’s a great source of calcium, a mineral that not only builds healthy bones, but also helps regulate heart rate, allows muscles to contract, and supports normal blood clotting. 

Yet while many of us grew up with a refrigerator that almost always featured a carton of milk front and center, plenty of us don’t think much about calcium as adults—and may fall short on this critical micronutrient. (FYI: Postmenopausal women and those who don’t eat much dairy, which is a lot of people these days, are at the greatest risk here.)

Other than breaking a bone—which we’d really rather you not do—various signs and symptoms can indicate that your calcium levels have dropped. Here are six sneaky signs of low calcium to watch out for. 

• ABOUT OUR EXPERTS: Emily Maus, R.D., a registered dietitian with Live Well Dietitian and nutrition consultant for Consumer Health Digest who specializes in women’s hormones. Dr. Alaa Gerais, N.M.D., is a doctor of naturopathic medicine with Sonoran University of Health Sciences in Arizona.

1. Hardcore PMS

It’s normal to feel moody in the days leading up to menstruating, but if you find yourself bloating up like a balloon and weeping over all the little things, a nutrient deficiency could be the culprit. “Studies indicate that low levels of calcium could be a predictor of PMS symptoms of low mood, fatigue, and bloating,” says Emily Maus, R.D., a registered dietitian with Live Well Dietitian and nutrition consultant for Consumer Health Digest who specializes in women’s hormones. “Adequate levels of calcium are needed to release the mood-regulating hormone serotonin. If calcium levels are low, menstruating females are more likely to suffer from depression, anxiety, anger, and irritability.”

That’s why Maus recommends menstruating women load up on calcium (among a few other specific nutrients!) before their menstrual cycle. Turn to dairy products, broccoli, seeds, sardines, and almonds, or consider a calcium supplement to fulfill even more of your daily needs.

2. Dental Problems

Your teeth aren’t made of bone, but just like bones, they’re affected by calcium levels. If the calcium in your bloodstream takes a nosedive, you might end up with weak teeth that break, decay, and even fall out.

Read More: How to Keep Your Chompers in Check–the Natural Way

The connection here has been long-established. For example, one older study from 2001 found a direct link between poor calcium intake and tooth loss in people aged 65 and older. People whose intake was sufficient were significantly less likely to lose their chompers than those who didn’t take in enough. In other words, a glass of milk (or supplement) a day could keep the dentist away.

3. Dry Skin 

Is your dry, flaky skin due to the changing of seasons—or the result of a calcium deficiency? According to naturopath Dr. Alaa Gerais, N.M.D., of Sonoran University of Health Sciences in Arizona, calcium plays a role in maintaining smooth, moisturized skin. “Calcium helps the skin barrier maintain its proper pH balance, which allows the skin to stay moisturized,” she explains. Bet you haven’t heard that one before! 

Read More: 10 Ways You’re Drying Out Your Skin Without Even Realizing It

Besides grabbing the right skin-care products, Gerais recommends keeping skin moisturized by drinking plenty of water and consuming sufficient electrolytes (surprise: calcium is an electrolyte!). Incorporating an electrolyte powder into your hydration routine is an easy way to get in more of these important minerals and H2O.

4. Brittle Nails

Much like brittle bones and teeth, brittle nails can be a hallmark of low calcium. (Though most calcium is contained in the skeleton, some is stored in the nails.) But what exactly do “brittle” nails look like? “Signs to look for in your nails are slow growth, easy breakage, or nails that split or crack from the tips,” Maus says. “You may notice your nails cracking after doing the dishes or working with your hands.” If your nail problems become more severe than a manicure can fix, consider talking to your doctor about your levels of this must-have mineral.

5. Muscle Cramps

At some point, most of us have experienced the unique misery of a running cramp or a nighttime charley horse. If you get these frequently, though, they can put a real, well, cramp in your sleep or workout routine. 

To outwit painful muscle contractions, you may want to check in on your calcium intake. “Calcium is needed to control the reaction between two fibrous filaments involved in muscle contraction. When this mineral is low, it causes the two proteins (myosin and actin) to contract easily, causing muscle cramps,” Maus says. 

6. Fatigue 

Fatigue can have dozens of causes, so feeling sluggish doesn’t necessarily merit an instant blood test to check on your calcium. Still, when combined with other symptoms on this list, tiredness—especially muscular fatigue—might point to problems with your levels. “Since calcium is used to help skeletal muscles contract, deficiency can cause muscular fatigue, making you feel tired,” Gerais explains.

And get this: Low calcium might not cause physical fatigue alone. It could be behind the feeling of mental fog, too. “Calcium is also needed for nerves to communicate, so when there is a deficiency, nerve firing can slow, causing mental fatigue,” adds Gerais.

Think You’re Low On Calcium? Here’s What To Do

The only way to know whether your calcium levels have dipped is to get a blood test. So if you’re concerned you may be deficient, start there.

In the meantime, though, it’s never a bad idea to ramp up on healthy, whole foods that contain plenty of calcium. “Include more calcium-rich foods by adding foods like yogurt, cheese, fortified soy products, almonds, and leafy greens,” Maus recommends. For reference, both athletes and sedentary adults aged 19 to 50 should strive for 1,000 milligrams of calcium per day. (A serving of plain, low-fat yogurt contains about 415 milligrams, while a serving of canned bone-in sardines offers 325 milligrams.)

While you’re at it, be sure to add foods that contain vitamin D, too. According to Gerais, calcium deficiency isn’t all that common by itself—instead, it’s usually linked to vitamin D deficiency, which can lead to calcium losses because it’s needed for proper absorption. Some high-vitamin D foods include fortified dairy and orange juice, fatty fish, egg yolks, and mushrooms.

In some cases, adding a supplement may be a good bet for getting enough of these two nutrients. “Although adequate calcium can be consumed through diet, supplementation may benefit some individuals, including those with bone health concerns, people who limit or avoid dairy products, or those who struggle to absorb nutrients, such as those with gut health issues,” Maus says. It’s worth a chat with your doctor to see if supplements (both calcium and vitamin D) are a good fit for you.