Vitamin D deficiency is not a rare problem in the United States. In fact, it is estimated to affect around 8 percent of the population, making it the third most common nutrient deficiency in the country.

It can be addressed by increasing exposure to sunlight, including more of certain foods in your diet, or speaking to a doctor about the possibility of taking supplements. Here are some of the health problems that have been linked to this deficiency.

1. Weaker bones

Vitamin D plays an important role in bone health as it helps our body with the absorption of calcium. The consequences of a deficiency are "secondary hyperparathyroidism and bone loss, leading to osteoporosis and fractures, mineralization defects," as noted by research over the years.

If you are experiencing bone and joint pain, it might be a sign that your body needs more vitamin D. Postmenopausal women, who are said to be an at-risk group, are more likely to experience back pain if they have a deficiency. Children are also more likely to have weaker enamel if their mothers had a deficiency while pregnant.

2. Loss of hair

Shedding 50 to 100 strands of hair per day is actually normal, according to the American Academy of Dermatologists. If the amount of hair falling out seems more severe, it may be a sign of inadequate vitamin D levels.

An autoimmune disease known as alopecia areata, which attacks hair follicles, has also been associated with this deficiency. One study, which examined patients with the disease, suggested an influence in severity — the lower the levels of the vitamin in the body, the more hair loss a person may experience.

3. Cognitive decline

While the exact mechanism has not been established, a new study from the University of Queensland suggested that low vitamin D levels may reduce perineuronal nets in the hippocampus — the brain region which is related to memory formation.

In a press release, Thomas Burne, a Queensland professor who led the study, said this may contribute to a loss of cognitive function which could be tied to conditions like Alzheimer's disease or schizophrenia. 

4. Poor bladder control

Aside from the softening of the bones, studies have also linked low levels of vitamin D with reduced muscle strength. Health.com notes that this may result in the weakening of the pelvic floor i.e. the muscles that support the bladder, vagina, uterus, and rectum.

This weakening has been linked to urinary and fecal incontinence in case reports and observational studies, though better quality research is needed to determine the severity. "For women who suffer from poor bladder control, maintaining healthy levels of vitamin D could prove to be as important as performing pelvic floor exercises," the website added.