In addition to giving you cancer and other horrible lung diseases, smoking rots the brain by damaging memory, learning and reasoning, according to a new study.
King's College London looked at 8,800 people over 50 who showed high blood pressure and were overweight, but who also showed neurological effects.
Researchers, who said lifestyles impact the mind as well as the body, were investigating links between the likelihood of a heart attack or stroke and the brain.
Data was collected and brain tests, such as making participants learn new words or name as many animals as they could in a minute, were also performed.
They were all tested again after four and then eight years.
Results showed that the overall risk of a heart attack or stroke was "significantly associated with cognitive decline" with those at the highest risk showing the greatest decline.
It also said there was a clear "consistent association" between smoking and lower scores in the tests. One of the researchers, Dr. Alex Dregan, said:
"Cognitive decline becomes more common with ageing and for an increasing number of people interferes with daily functioning and well-being.
"We have identified a number of risk factors which could be associated with accelerated cognitive decline, all of which, could be modifiable."
The doctor added in conclusion: "We need to make people aware of the need to do some lifestyle changes because of the risk of cognitive decline."
Researchers do not know how such a decline could affect people's daily lives, nor whether an early drop in brain function could lead to conditions such as dementia.
Dr Simon Ridley, from Alzheimer's Research UK, said:
"Research has repeatedly linked smoking and high blood pressure to a greater risk of cognitive decline and dementia, and this study adds further weight to that evidence."
"Cognitive decline as we age can develop into dementia, and unraveling the factors that are linked to this decline could be crucial for finding ways to prevent the condition."
"Eating a balanced diet, maintaining a healthy weight, exercising regularly, getting your blood pressure and cholesterol checked and not smoking can all make a difference."