Fertility, regular mensesPatient friendly summary

  • Sunlight affects fertility in two ways: (1) UVB generates vitamin D, and (2) blue light from the sun and TVs and computer screens lowers melatonin production.
  • Vitamin D and melatonin may reduce the risk of infertility for females and males.
  • Fertility may be enhanced by mid-day sun exposure and less evening blue light.

Infertility is the inability to produce a child, generally after a year of trying. Infertility also includes frequent miscarriages.

Infertility may be equally linked to:

  • the woman,
  • the man,
  • both the woman and man,
  • or no known cause.

Risk factors

Common causes of female infertility include:

  • Ovulation problems
  • Tubal blockage or tubal ligation (tubes tied)
  • Age-related factors
  • Uterine problems

The main cause of male infertility is low semen quality.

Sunlight exposure and infertility risk

Sunlight appears to help regulate fertility. In animal studies, the length of daylight is the key factor in fertility. Many animals are born in the spring, when food is more readily available.

Sunlight primarily affects production of melatonin rather than vitamin D. Melatonin is a hormone mainly produced by the absence of bright blue light. This hormone controls the body’s 24-hour internal clock of sleeping and waking. This is called the circadian rhythm. When it is dark, the body produces melatonin, which triggers sleep. When it is light, the body makes less melatonin.

Melatonin also affects secretion of the luteinising hormone. This hormone controls female ovulation and male sperm production. Lower ovarian activities are noted in winter, when there is more melatonin.

Studies were done at an in vitro fertilization clinic in Israel. The highest fertilization and quality-A embryo rates were observed in the spring, when there is more sunlight. The lowest were noted in the fall, when there is less sunlight.

Vitamin D and infertility

Vitamin D levels

In Turkey, women with higher vitamin D levels had more successful in vitro fertilization. Each 1 ng/mL (2.5 nmol/L) increase of vitamin D was linked to a 6% increase in clinical pregnancy.

However, in Greece, women with higher vitamin D levels (more than 30 ng/mL [75 nmol/L]) had half the pregnancy success rate from in vitro fertilization of those with lower values. The quality of the embryos was also lower. Follicular fluid vitamin D explained only 7% of the variation in embryo quality, which is a small effect.

Thus, it is not clear whether vitamin D affects pregnancy rates.

How vitamin D works

Vitamin D may affect infertility by:

  • Reducing inflammation and the production of inflammatory cytokines, which lowers the risk of miscarriage
  • Enhancing sperm structure and motility, which improves fertilization

How melatonin works

Melatonin may affect infertility by:

  • Adjusting circadian rhythm
  • Adjusting hormones and immune system
  • Protecting cells in pregnancy
  • Correcting complications during pregnancy due to abortion, pre-eclampsia, or fetal brain damage


Vitamin D may lower the risk of infertility for both females and males. Based on studies of various diseases, vitamin D levels of 30-40 ng/mL (75-100 nmol/L) may be linked to better outcomes.


Melatonin production may improve fertility and pregnancy outcomes. There are no guidelines for supplementation. However, melatonin is produced when the eyes receive less bright blue light. Therefore, it may be helpful to reduce exposure to blue radiation in evenings. The primary sources are televisions and computer screens.


One study researched vitamin D treatments for polycystic ovary syndrome, a common hormone problem. Treating women with 400 international units (IU) (10 mcg)/day vitamin D, 1000 mg/day calcium, and 1500 mg/day metformin (blood sugar stabilizer) increased the number of large follicles after 2–3 months. (Ovarian follicles house human eggs as they mature.) This combination was more effective than treatments of either vitamin D plus calcium or metformin.

Find out more...

We will be adding a detailed evidence summary on this topic in the near future.  Please check back soon to find out more.

Page last edited: 17 May 2011