The benefits of vitamin D, backed up by tons of research, ring loud and clear: strong bones, improved mood, even more efficient weight loss. But signs that you’re low on the nutrient are a bit quieter. If you notice one or more of these issues, head to your physician to get your blood tested. (But don’t reach for supplements quite yet—you’ll want to make sure it’s a vitamin D deficiency you’re dealing with first since excessive intake of the nutrient can be linked to its own health concerns.)
1. Muscle Weakness
Decreased muscular size can be the result of not enough vitamin D in muscle and nerve tissue, says Kimberly Mueller, R.D., owner of Fuel Factor Nutrition Coaching. So if you notice that you can’t eek out the same number of reps you’ve always done, that may be a sign you need more vitamin D.
According to a study in The Journal of Clinical Endocrinology & Metabolism, women with low levels of D are twice as likely to combat depression.
3. Greater Pain Sensitivity
Insufficient levels of vitamin D have been linked to chronic pain, especially in black Americans.
4. Stress Fractures
Vitamin D promotes bone growth—but when you’re low in the nutrient, your bones become weakened, meaning your risk for stress fractures increases, says Mueller. In fact, some studies show as high as double the risk if vitamin D levels are exceptionally low.
5. High Blood Pressure
Vitamin D plays a role in heart health, helping to regulate blood pressure. So when you don’t get enough, your blood pressure can creep up.
In one 2012 study published in the Journal of Clinical Sleep Medicine, lower levels of vitamin D were linked to higher levels of daytime sleepiness.
Before you blame your grouchiness on PMS, know that D affects the levels of serotonin in your brain—which also impacts your mood.
8. Decreased Endurance
Some studies have shown reduced aerobic capacity and overall endurance in athletes with low vitamin D levels, says Mueller.