It can also increase your risk of diabetes, heart disease and obesity, as well as cause clinical depression.
She said lonely people tended to have higher inflammation and anxiety levels than others, and also be less active, both contributing to worse health.
But the researchers also claimed the increased levels of stress caused by loneliness could also be boosting the risk.
Writing in the journal, Dr Angelina Sutin and colleagues said: 'Loneliness has recently been identified as a significant public health problem but one that can be addressed with financial and institutional support. .
'The research highlights one poor outcome associated with loneliness: Individuals with loneliness are more likely to develop dementia than less lonely individuals. .
Doubles the risk of type 2 diabetes .
Loneliness could double a person's risk of developing type two diabetes because it can create a 'long-lasting state of distress', experts say.
The Norwegian team analysed health information of more than 24,000 people, 1,179 of whom went on to develop type two diabetes, via population surveys between 1995 and 2019.
The findings, published in the European Association for the Study of Diabetes's journal Diabetologia this week, showed that higher levels of loneliness were strongly associated with a higher risk of type two diabetes when measured 20 years later.
After adjusting for age, sex and education level the team found that participants who responded 'very much' were twice as likely to develop type two diabetes than those who did not feel lonely.
Writing in the study, the team at Western Norway University of Applied Sciences in Bergen, said: 'This study suggests that loneliness may be one factor that increases the risk of type 2 diabetes.
'We recommend that loneliness should be included in clinical guidelines on consultations and interventions related to type 2 diabetes.'.
Loneliness increases the risk of older women developing potentially deadly heart problems, a study has found.
The subjects were asked about their level of loneliness and social isolation, and this was compared with rates of heart disease
The study found that women who were both lonely and isolated were between 13 and 27 per cent more likely to be diagnosed with heart disease
The research, published in the journal Jama, warned that increased isolation caused by Covid-19 and lockdowns may have put more older women at risk of heart problems
Ensuring people are less lonely could also help reduce their risk of heart problems, such as stroke
British researchers found having poor social relationships increased the chance of coronary heart disease (CHD) by 29 per cent
But previous research has also linked heart disease to stress and inflammation — a collateral effect of loneliness
The team behind the latest research said public health policy should aim to address social isolation to prevent the two deadly diseases.
The studies measured social isolation and loneliness in participants.
The researchers said: 'The main finding of our review, that isolated individuals are at increased risk of developing CHD and stroke, supports public health concerns over the implications of social relationships for health and well-being.
'Our work suggests that addressing loneliness and social isolation may have an important role in the prevention of two of the leading causes of morbidity in high-income countries.'
They said: 'While some studies point to an association between obesity and increased loneliness levels, it should be acknowledged that findings are mixed