Why we should take a women-centred approach to diagnosing and treating iron deficiency
Researchers have investigated many factors that influence iron levels, such as diet and exercise, but we still don't fully understand the role that women's reproductive hormones play in regulating iron uptake, writes Claire Badenhorst of Massey University in this republished article from The Conversation.
Iron deficiency is a common nutritional disorder around the world, and pre-menopausal women are the most likely to be diagnosed with it.
According to the most recent nutritional survey conducted in New Zealand (2008/09), 12 percent of women may be iron deficient. However, new research from New Zealand suggests that up to 55% of women of a similar age but of different ethnicities (Caucasian, Middle Eastern, and South Asian) have iron deficiency.
This higher prevalence of iron deficiency in women is frequently attributed to blood loss during menstruation. However, my study of the iron status of athletic and active women suggests that female physiology has evolved to counter iron loss via complex interactions between female reproductive hormones and the hormone that influences iron regulation.
The study found that iron status varies during a woman's monthly cycle, and we recommend that doctors take note of the phase of the menstrual cycle a woman is in when performing iron-screening blood tests. Furthermore, before interpreting test results, they should ask women if they have a natural menstrual cycle that is not influenced by hormonal contraceptives (pill or IUD).
Iron in the body
Iron is essential for good health and well-being. It is a component of haemoglobin, the pigment found in red blood cells that transports oxygen throughout the body.
Even though iron is necessary for healthy and normal functioning, we cannot produce it and must instead rely on recycling it within the body and obtaining it from food. Whole grain cereals, legumes, fish, poultry, and meat are all good sources of iron.
Iron is well controlled and regulated by the body. The daily iron loss is only 1-2mg. According to research, women will lose an additional 1mg of iron per day of menstruation, bringing the total iron loss to 3-5mg during menstrual blood loss (which may last 1-5 days). This can be exacerbated in women who have heavy or prolonged menstrual bleeding.
Hepcidin is the primary iron regulatory hormone. It works on the body's only known iron export channels, which are found in the small intestine (iron absorption from foods), the surface of white blood cells (iron recycling in the body), and liver cells (iron release from its reservoir in the liver).
Higher levels of hepcidin cause the iron export channels to degrade, effectively stopping the movement of iron from the gut and its release from storage sites. This also reduces the body's ability to recycle iron from dead red blood cells, either for production of new red blood cells or storage in the liver.
Female physiology and iron status
Only two studies have been conducted to date to investigate the changes in iron status and hepcidin in premenopausal women throughout the menstrual cycle.
My research shows that hepcidin (and other iron-related factors) drop dramatically during menstruation (days 1-5 of the monthly cycle). Hepcidin remains low for a few days after menstruation and then gradually increases until ovulation (at about day 14).
Hepcidin appears to increase and plateau after ovulation as women enter their luteal phase (days 15-28), before repeating the cycle the following month.
Oestrogen suppresses hepcidin activity, whereas progesterone stimulates it, according to research using isolated cells and studies with women undergoing in-vitro fertilisation. This explains why hepcidin levels are low during the follicular phase (days 1-14 of the menstrual cycle) and rise during the luteal phase (days 15-28).
These findings suggest that, in response to blood loss, which accelerates iron loss, female physiology is primed to maximise iron absorption in the first half of the menstrual cycle by lowering hepcidin activity. This may be a physiological response to menstrual blood loss.
A few studies have also shown that serum iron, transferrin, and haemoglobin — all markers used to assess an individual's iron status — fluctuate throughout the menstrual cycle. According to one study, 23 percent of women were iron deficient during menstruation, but this dropped to 8 percent during the luteal phase.
The percentage of iron transported and used in the body is measured by transferrin saturation. Some women may reach transferrin saturation levels of 45 percent during the luteal phase, when iron levels may rebound. This is usually due to an excess of iron or haemochromatosis, a genetic disorder that causes excessive iron absorption and storage, which can be toxic to vital organs.
Some may argue that research into iron deficiency is well established, and that we have covered all of our bases in terms of detecting and treating this micronutrient deficiency. However, iron levels are low in 18-55 percent of pre-menopausal women in New Zealand.
Many lifestyle factors, such as dietary preferences, meat consumption, and exercise, have been studied by researchers. However, we have yet to fully consider female physiology and how the menstrual cycle influences the complexities of iron deficiency diagnosis and treatment.
At a time when many people are calling for women-centred research to identify specific health outcomes and treatments, it may be time to reopen the iron deficiency box.