Lack of sleep six months after having a baby can add up to seven years to the biological age of new mothers, a study has found.

       Researchers said that when new mothers complain of sleepless nights taking years off their life, they just might be right. The lack of sleep could also leave them more susceptible to cancer and cardiovascular disease.

       Women having less than seven hours sleep a night – because they are constantly attending to their newborns – could see them gain three to seven biological years, the study found.

       Scientists studied 33 mothers during their pregnancies and the first year of their babies’ lives, analysing their DNA from blood samples to determine their “biological age” – which can differ from chronological age.

       They found that a year after giving birth, the biological age of mothers who slept less than seven hours a night at the six-month mark was three to seven years older than those who logged seven hours or more.

       Mothers who slept less than seven hours also had shorter telomeres in their white blood cells. These small pieces of DNA at the ends of chromosomes act as protective caps, like the plastic tips on the ends of shoelaces, scientists said. Shortened telomeres have been linked to a higher risk of cancers, cardiovascular and other diseases, and earlier death.

       Judith Carroll, professor of psychobiology at UCLA and the study’s first author, said: “The early months of postpartum sleep deprivation could have a lasting effect on physical health.

       “We know from a large body of research that sleeping less than seven hours a night is detrimental to health and increases the risk of age-related diseases.”

       While participants’ nightly sleep ranged from five to nine hours, more than half were getting less than seven hours – both six months and one year after giving birth, the researchers found.

       Prof Carroll added: “We found that with every hour of additional sleep, the mother’s biological age was younger. I, and many other sleep scientists, consider sleep health to be just as vital to overall health as diet and exercise.”

       Prof Carroll urged new mothers to take advantage of opportunities to get extra sleep, like taking naps when their babies are asleep, accepting offers of help from family and friends, and asking partners to help during the night or early morning.

       She said: “Taking care of your sleep needs will help you and your baby in the long run.”

       Christine Dunkel Schetter, co-author and professor of psychology and psychiatry at UCLA, said: “The study results and other findings on maternal postpartum mental health provide impetus for better supporting mothers of young infants so that they can get sufficient sleep – possibly through parental leave so that both parents can bear some of the burden of care, and through programmes for families and fathers.”

       Prof Dunkel Schetter added that while accelerated biological aging linked to sleep loss may increase women’s health risks, it doesn’t automatically cause harm to their bodies.

       She added: “We don’t want the message to be that mothers are permanently damaged by infant care and loss of sleep. We don’t know if these effects are long lasting.”

       The study used the latest scientific methods of analysing changes in DNA to assess biological ageing – also known as epigenetic aging.

       DNA provides the code for making proteins, which carry out many functions in the cells of our body, and epigenetics focuses on whether regions of this code are “open” or “closed”.

       Prof Carroll said: “You can think of DNA as a grocery store, with lots of basic ingredients to build a meal.

       “If there is a spill in one aisle, it may be closed, and you can’t get an item from that aisle, which might prevent you from making a recipe. When access to DNA code is ‘closed’, then those genes that code for specific proteins cannot be expressed and are therefore turned off.”

       Because specific sites within DNA are turned on or off with ageing, the process acts as a sort of clock, allowing scientists to estimate individuals’ biological age, Prof Carroll said.

       The greater an individual’s biological, or epigenetic age, the greater their risk of disease and earlier death, the researchers warned.

       The study’s subjects – which included women who ranged in age from 23 to 45 six months after giving birth – is not a large representative sample of women, the study authors said.

       It means more studies are needed to better understand the long-term impact of sleep loss on new mothers, what other factors might contribute and whether the biological aging effects are permanent or reversible, they added.

       Prof Carroll and Prof Dunkel Schetter reported last year that a mother’s stress prior to giving birth may accelerate her child’s biological ageing, which is a form of “intergenerational transfer of health risk”.

       The UCLA research was published in the journal Sleep Health.