Germ cell maturation and fertilisation —
Selenium, zinc and the EU evidence base

Selenium in the context of sperm formation

Glutathione peroxidase 4 and the capsule proteins of sperm

The glutathione peroxidase family comprises eight known isoforms, of which GPx4 (also called PHGPx) is the only one able to reduce hydroperoxides directly in membrane lipids. In testicular tissue, GPx4 is expressed at particularly high concentrations in the late spermatids.

During the maturation of sperm, GPx4 changes from a soluble enzyme into an insoluble structural protein. It is built into the midpiece capsule — the structure that encases the mitochondria of the sperm cell and enables the motility of the flagellum. This conversion presupposes the availability of selenium as selenocysteine.

Selenium-rich foods and the EU reference value

The reference value for daily selenium intake under EU Regulation 1169/2011 is 55 µg. Actual intake depends strongly on the selenium content of the soils on which cereals and forage crops are grown — a factor that varies considerably within Europe.

The bioavailability of selenomethionine from animal products is generally higher than that of selenite from inorganic sources. At the same time, a high vitamin C intake can promote the reduction of selenite in the stomach and affect its absorption.

Zinc, fertility and reproduction

Zinc in the chromatin condensation of the sperm head

During spermiogenesis — the final differentiation phase — the histones in the cell nucleus are gradually replaced by protamines. Zinc ions form bridges between the thiol groups of neighbouring protamines and thereby create a dense, stable packaging of the paternal DNA. This process, chromatin condensation, matters for the mechanical resilience and the fertilising capacity of the sperm.

Zinc is also involved in regulating the enzyme 5α-reductase, which converts testosterone into its more potent form dihydrotestosterone. The prostate contains the highest zinc concentration of all soft tissues — a fact that documents the reproductive significance of this trace element.

Zinc sources and daily requirements

The reference value for daily zinc intake in the EU is 10 mg. The bioavailability of zinc from animal foods is generally higher than from plant sources, because phytic acid in cereals and pulses can reduce absorption in the small intestine.

Soaking and sprouting pulses and cereals can reduce the phytic acid content and thereby favour zinc absorption. Taking animal protein at the same time increases the absorption rate further, because amino acids such as histidine act as zinc ligands.

From germ cell to fertilisation — the biological framework

The 74-day cycle of spermatogenesis

In humans, the formation of a mature sperm cell from a spermatogonium takes an average of 74 days. This period is divided into three phases: the mitotic proliferation phase (spermatogoniogenesis), the meiotic maturation division (spermatocytogenesis) and the morphological remodelling (spermiogenesis). Specific enzymes are active in each phase, and their cofactor requirements presuppose the availability of certain trace elements.

The hormone axis and mineral-dependent enzymes

The hypothalamic-pituitary-gonadal axis controls male reproduction via the hormones GnRH, FSH and LH. LH stimulates the Leydig cells to produce testosterone, while FSH activates the Sertoli cells, which act as nurse cells for the maturing sperm. Both testosterone synthesis and Sertoli cell function involve zinc-dependent enzyme steps.

Absorption, distribution and interactions

Selenium is absorbed in the small intestine predominantly as selenomethionine, with an absorption rate of between 70 % and 90 % where protein intake is adequate. In the blood, selenium binds to selenoprotein P, which acts as a transport protein and carries the trace element into various target tissues — including the testes.

Zinc is absorbed mainly in the jejunum, with the absorption rate varying between 15 % and 40 % depending on the composition of the food. High calcium intake and phytic acid can reduce zinc absorption, while animal protein favours it.

Taking both trace elements at the same time in customary doses corresponding to the EU reference values is harmless according to current knowledge. At markedly excessive doses, interactions can occur — for example, a very high zinc intake can affect selenium retention. The recommended daily intake should therefore not be exceeded.

Open points and follow-up questions

How is selenium status measured in the blood?

Selenium status can be determined via the plasma selenium level or the activity of glutathione peroxidase in whole blood. Both parameters are obtained by a physician through a blood test. The plasma selenium level reflects short-term supply, while GPx activity allows conclusions about longer-term status.

Does the chemical form of zinc affect absorption?

Zinc occurs in dietary supplements in various chemical forms — for example as zinc gluconate, zinc picolinate or zinc oxide. Studies show different absorption rates depending on the compound, with organic zinc salts tending to be absorbed better than inorganic ones. The authorised EU claim refers to zinc irrespective of the chemical form.

What does “normal spermatogenesis” mean in the EU sense?

The term “normal” in the EFSA claims describes the physiologically proper function where supply of the mineral concerned is adequate. It is not a therapeutic efficacy statement. The claim was authorised on the basis of scientific opinions from EFSA and refers to the general adult population.

Is there a connection between diet and male fertility?

The scientific literature documents relationships between the supply of certain micronutrients and parameters of semen quality. EU Regulation No 432/2012, however, permits only those claims that have been authorised through a strict assessment procedure by EFSA. Individual health questions should always be discussed with a physician.