Women with fibromyalgia are more likely to have iron deficiency than women who do not have the disease, a study has found.

The study, “Association of ferritin levels with depression, anxiety, sleep quality, and physical functioning in patients with fibromyalgia syndrome: a cross-sectional study,” was published in the Croatian Medical Journal.

Lack of iron (iron deficiency) in people with fibromyalgia may contribute to chronic fatigue, muscle pain, decreased endurance, and sleep disturbances. It also may lower an individual’s pain threshold, increasing sensitivity to pain, which is one of the hallmarks of the condition.

A previous case-control study showed that patients with fibromyalgia had lower levels of ferritin — a protein that is responsible for storing iron in the body — than healthy individuals. Notably, “Serum ferritin concentration (cut-off <30 ng/mL) is the most sensitive and specific test for iron deficiency,” the authors wrote.

However, no study has explored the potential relationship between low levels of ferritin in the blood and sleep quality among those with fibromyalgia.

For that reason, researchers from the Tokat State Hospital in Turkey and their collaborators set out to assess the frequency of iron deficiency in women with and without fibromyalgia, as well as to explore the possible relationship between low levels of ferritin and typical symptoms of fibromyalgia, including depression, anxiety, and poor sleep quality.

The cross-sectional study included data from 100 women with fibromalyagia and 100 women without the disease who were approximately the same age (controls). Ferritin levels were measured in all study participants from 2016 to 2017 at the hospital. Women with ferritin levels lower than 30 ng/mL were considered to have iron deficiency.

Participants with fibromyalgia also were asked to complete a series of questionnaires to evaluate the severity of their disease (Fibromyalgia Impact Questionnaire), as well as the extent of their depression (Beck Depression Inventory), anxiety (Beck Anxiety Inventory), and sleep quality (Pittsburgh Sleep Quality Index).

Findings revealed the percentage of women with iron deficiency was significantly higher among those with fibromyalgia than those who did not have the disease (64% versus 42%). Moreover, the median levels of ferritin were lower in women with fibromyalgia than in controls (20.95 ng/mL versus 34.91 ng/mL),

Statistical analyses found no relationship between ferritin levels and the degree of anxiety, depression, and sleep quality in women with fibromyalgia. However, among those who had poor sleep quality, lower ferritin levels were found to be associated with higher levels of depression.

“This finding could be explained by the fact that iron is needed for the synthesis [production] of neurotransmitters involved in depression pathogenesis [development],” the researchers wrote. Neurotransmitters are chemical substances that allow nerve cells to communicate with one another.

“[T]he results of our study [also] point to the fact that FMS [fibromyalgia] patients should have their ferritin levels evaluated, since iron deficiency treatment could prevent the deterioration of their clinical condition,” they added.