8 Seemingly Impossible Things Your Birth Month Could Predict About Your Future Health

When you were born could play a fascinating role in everything from your risk of melanoma to food allergies, science suggests.

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Your birthday dictates your zodiac sign, but new research suggests that it may also affect various aspects of health later in life. Keep in mind: The impact of birth season is far from definitive; heredity and environment play a far bigger role.

Fall Birthdays

1. Better physical fitness: A study in the International Journal of Sports Medicine found that school-age boys born in November scored an average of ten percentile points higher on tests of cardiorespiratory fitness, handgrip strength, and lower-body power compared with those born in April. Fall babies’ mothers are pregnant in the summer, when vitamin D levels surge. Vitamin D affects fetal physical development.

2. Food allergies: People with autumn birthdays were 30 to 90 percent more likely to develop food allergies than those born in other seasons, according to Johns Hopkins University research. Fall babies are exposed to less skin-protecting vitamin D early in life, which could make them more likely to develop a sensitivity to food allergens through the skin.

Winter Birthdays

3. Left-handedness: Men born during this season are more likely to be lefties than those born during other times of the year, according to new Austrian and German research. High levels of testosterone in utero can make left-handedness more likely—and longer periods of daylight during the summer can trigger a testosterone surge at a crucial time during fetal development when handedness might be influenced.

4. Premature birth: Babies conceived in May (and typically born in February) are 10 percent more likely to arrive prematurely than those conceived during other seasons, a 2013 study found. Expectant mothers’ exposure to flu in the last trimester may be why. Pregnant women should get vaccinated for flu.

Spring Birthdays

5. Melanoma: Spring-born people have a 21 percent greater chance of developing melanoma than those born in the fall, reported a 2014 study in the International Journal of Epidemiology. Exposure to UV light during the first few months of life may affect the body’s susceptibility to developing melanoma as an adult. That said, lifelong habits— using sunscreen year-round, not tanning, wearing hats and sunglasses—go a long way toward protecting you against all forms of skin cancer.

6. Earlier menopause: In an Italian study of nearly 3,000 postmenopausal women, those born in spring were more likely to reach menopause just before age 49; those born in the fall were likelier to enter menopause about 15 months later. Fall women might be born with a greater number of eggs.

Summer Birthdays

7. Nearsightedness: Summer babies are more prone to need glasses for distance, found a study in the journal Ophthalmology. This may be because of the amount of light babies are exposed to right before and after they’re born. Research in animals has shown this can affect normal eye development.

8. Mood swings: People born during summer months are more likely to have “cyclothermic temperament,” or rapid fluctuation between sad and happy moods. Light and temperature exposure may affect brain chemicals that regulate mental health.

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