Vitamin D plays a big role in keeping bones strong and helping the body absorb calcium … and not having enough of it can lead to a whole slew of ailments. Vitamin D deficiency can increase the risk for everything from cardiovascular disease to asthma. Now, experts say vitamin D deficiency could also be a cause for infertility.

A study published in the Journal of Clinical Endocrinology & Metabolism found that women with healthy levels of vitamin D are twice as likely to get pregnant than those with vitamin D deficiency. Those getting enough vitamin D also had higher-quality embryos that seemed to have a better chance of implanting in the uterus.

Overall, vitamin D deficiency almost doubled from 1994 to 2004. More than 40 percent of women in child-bearing age aren’t getting enough of this crucial nutrient. Vitamin D plays a key role in how cells function, and even whether they live or die. Lack of vitamin D has also been linked with other pregnancy problems, like gestational diabetes and hypertension.

So how do you know if you’re lacking D … and how much is enough? The signs are subtle, but bone pain and muscle weakness could signal something’s missing. People who are obese, have dark skin that limits absorption of sunlight and are older are also at risk.

Adults need up to 600 IUs of vitamin D daily. The nutrient is produced naturally by your body when you are exposed to sunlight, but that’s not always an option. Foods such as fatty fish, fortified dairy products like yogurt and milk, cheese and egg yolks are solid sources. But that still might not be enough. Your best bet is to take a daily supplement in pill form to be sure you’re getting all 600 IUs.

If you’re looking to get pregnant or just looking to improve your overall health, check with your doctor if a vitamin D supplement is right for you.