A body mass index (BMI) above 30 is linked to reduced male fertility. A high-fat diet and/or obesity may affect spermatozoa structure in a number of ways, including due to decreases in testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels and increased oestrogens.

Obesity may also be associated with disorders on the hypothalamic-pituitary-gonadal axis in some men.^1,4

Infertility relating to pituitary gland problems is usually due to a benign pituitary tumour. This can lead to reduced or absent LH secretion (decreasing testosterone production) and/or FSH (impairing spermatogenesis). Hormonal imbalances involving thyroid or prolactin can also reduce male fertility.^7,8,9

Hypogonadism with a low testosterone production can also occur due to tumours and genetics., such as the rare Kleinfelter syndrome where males carry an extra X chromosome (XXY). Another rare genetic disorder, Kallmann’s syndrome, affects the hypothalamus suppressing gonadotrophic releasing hormone (GnRH) secretion which then means the pituitary is not stimulated to secrete LH or FSH.^8,9,10,11

Undescended testes, previous testicular injury, testicular cancer, surgery or infection can reduce fertility, as can raised temperature in the scrotum, such as due to varicoceles (swollen veins in the scrotum), regular hot baths or saunas, or a recent fever.^9,12

Depression can lead to loss of libido, erectile dysfunction and ejaculation problems.¹²