Criminals are being sentenced to "worsened health" when they are sent to prison, a new report suggests.
The Health and Social Care Select Committee said poorer health is "too often the outcome" for inmates as a result of "overstretched staff, overcrowding and poor facilities".
MPs on the committee have penned a damning report on the state of health of people incarcerated in the nation's jails.
They said the Government is "failing" in its duty of care towards prisoners, with too many remaining in unsafe, unsanitary and outdated establishments.
Meanwhile, violence and self-harm are at record highs, the report adds.
Overcrowding, synthetic drugs and staff shortages have also been linked to poorer health outcomes for inmates.
The report also states that too many people are dying in custody or shortly after release.
The authors said jails could be an opportunity to "address serious health inequalities which are part of the cycle of disadvantage faced by people in prison".
They made a series of recommendations to help reduce health problems among prisoners.
They challenged the Government to name the date by which it expects to have enough prison officers in post to ensure the vast majority of inmates can be unlocked for the recommended 10 hours a day.
The report highlights that cells staff shortages have forced "overstretched" prisons to run "restricted regimes" which limit inmates' ability to "engage in purposeful activity" or access health and care services.
The MPs also said that the Government's programme of prison reform should place greater emphasis on health, well-being, care and recovery, recognising the poor health of people in jail and the trauma many people in prison have experienced in their lives.
"A prison sentence is a deprivation of someone's liberty, not a sentence to poorer health or healthcare," said Dr Sarah Wollaston, chairwoman of the Health and Social Care Committee.
"Too many prisons remain unsafe and unsanitary.
"Violence and self-harm is at a record high, with illegal drugs adding to the problems for both prisoners and staff.
"Poor living conditions, diet and restricted access to healthcare and activity are compounding a cycle of deprivation and health inequality.
"We need assurances from Government that it will urgently address the very serious situation in prisons with a whole-systems approach underpinned by sufficient funding and attention to the prison and healthcare workforce."
Commenting on the report, Bob Neill, chairman of the Justice Committee, said: "It is not right that prisoners suffer far worse health, especially mental health, than the general population.
"Reducing self-harm, which has reached a record high, and preventing self-inflicted deaths, must remain a Government priority.
"Healthy prison environments are integral to rehabilitation. Too often that is not the case.
"We have seen this repeatedly on recent prison visits, as well as examples where health professionals and prison governors work together to good effect."
A Government spokesman said: "We take our duty of care to prisoners and staff extremely seriously and have introduced a package of measures designed to make our prisons safe, decent and better able to manage the often complex health needs of offenders.
"This includes an extra £70 million to enhance the fabric of the estate and tackle the drugs which we know are fuelling violence, while up to 10,000 new prison places will provide conditions where healthcare can be delivered safely and efficiently.
"We have also recruited more than 3,500 new prison officers over the last two years and our new key-worker scheme means prisoners will receive intensive personal support throughout their sentence."
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