Nutrient Depletion in Perimenopause: What Is Actually Happening

Many women arrive at an appointment with a list of symptoms, are told it is perimenopause, and leave without a single blood test. For a significant number of them, sitting underneath the hormonal picture is something far simpler and far more fixable: a store that has run down. Here is how that actually works, and exactly where hormones enter the picture.

The precision worth starting with

It is often said that a hormone deficiency impairs the absorption of vitamins and minerals. That is partly true, and knowing where it is strong and where it is weaker changes what you do about it.

• For calcium and bone the link is well established. Estrogen and progesterone are both involved in bone turnover, with estrogen mainly restraining resorption and progesterone supporting new bone formation (Prior, 2018). When they shift, calcium and bone balance shift with them.
• For iron and B12 the mechanism is different. There the issue is usually not absorption but loss and depletion. And that is exactly what perimenopause produces.

Why then: in perimenopause ovulation becomes irregular, so there is less progesterone to balance estrogen. Prior and Hitchcock describe this stage as erratically higher estradiol together with decreased progesterone in anovulatory or short luteal phase cycles (Prior & Hitchcock, 2011). The practical consequence is familiar to many women: a thicker endometrium, and periods that become heavy and unpredictable. Every one of those cycles is iron going out the door.

And if you have given birth in recent years, that tap opened on a baseline that was already low. Pregnancy and lactation deplete iron, B12, and vitamin D before any hormonal change enters the picture. We cover that overlap in our guide to postpartum and perimenopause.

Iron: the loop with your thyroid

Low iron produces fatigue, breathlessness on exertion, palpitations, dizziness, and a tendency to feel weak on standing. That much is familiar. What is less familiar is that it also reaches the thyroid.

The enzyme that makes thyroid hormone, thyroid peroxidase, is heme dependent, meaning it requires iron. A review published in Thyroid states directly that iron deficiency impairs thyroid hormone synthesis by reducing the activity of heme dependent thyroid peroxidase (Zimmermann & Köhrle, 2002).

The practical meaning: "maybe it is iron" and "maybe it is thyroid" are not two competing hypotheses. Sometimes the first produces the second, which is why it is worth testing both together.

One note on ferritin: hemoglobin can come back entirely normal while iron stores are already empty. Ferritin reflects the store, and it is the one that tends to fall first. It is worth asking for it specifically rather than settling for "your blood count is normal".

Magnesium: the loop with vitamin D

Magnesium is involved in the electrical activity of the heart, in muscle function, in the nervous system, and in sleep. Which is why a shortfall can look remarkably confusing in midlife: tight muscles, palpitations, edginess, and broken sleep.

And there is a connection many people miss. A review by Uwitonze and Razzaque describes how all of the enzymes that metabolize vitamin D appear to require magnesium as a cofactor, in both the liver and the kidneys (Uwitonze & Razzaque, 2018).

In other words, if magnesium is low, vitamin D may not do what is expected of it even when it is being supplemented. That may explain why a vitamin D supplement alone sometimes underdelivers. For many women it makes sense to look at the two together rather than each in isolation.

Vitamin B12

Low B12 produces fatigue, brain fog, and sometimes numbness or tingling in the hands and feet. It is common after pregnancy and breastfeeding, in women eating plant based or vegan diets, and in those taking certain medications long term.

Why this matters especially here: brain fog is one of the symptoms women most often attribute to perimenopause, and it is also one of the classic presentations of low B12. Two possible explanations for exactly the same experience, and only a test separates them.

Why muscles and joints blur the picture further

A review published in Climacteric introduced a new term, the musculoskeletal syndrome of menopause, to describe the cluster of joint pain, loss of muscle mass, declining bone density, and progression of osteoarthritis in this period. The authors estimate that more than 70 percent of women will experience musculoskeletal symptoms through the transition, and that 25 percent will be disabled by them (Wright et al., 2024).

This is precisely where confusion sets in, because muscle pain, weakness, and cramping are also what low magnesium, vitamin D, or iron produce. Again, not either or. Usually it is a combination, and both parts deserve attention.

What is worth asking for

This is a list for a conversation with your clinician, not an instruction and not a prescription. Your clinician decides what is appropriate to test and how to interpret the results.

• Ferritin and a full blood count
• Vitamin B12
• Vitamin D (25-hydroxy)
• Magnesium and calcium
• TSH, free T4, and thyroid antibodies

One important caution: do not start an iron supplement on your own without testing. Excess iron is harmful, and some people carry a condition in which the body stores too much of it. Iron is taken according to a test and clinical guidance, not according to how you feel or a recommendation in a group.

And where do hormones fit

It is worth saying explicitly: correcting a nutrient deficiency does not cancel the hormonal transition, and the reverse is equally true. For many women both are happening at once and influencing each other. The useful direction is not to pick a side, but to bring your clinician both pictures together: the symptoms and how they behave across your cycle, and the bloodwork. We cover the role of progesterone itself in our guide to progesterone in perimenopause.

This content is for educational purposes only. Peritale is a general wellness product, not a medical device. It is not intended to diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional about your own health.