Our brains change with age, and mental function changes along with it. Mental decline is common, and it's one of the most feared consequences of aging. But cognitive impairment is not inevitable. Here are 12 ways you can help maintain brain function.

 
1. Get mental stimulation
Through research with mice and humans, scientists have found that brainy activities stimulate new connections between nerve cells and may even help the brain generate new cells, developing neurological "plasticity" and building up a functional reserve that provides a hedge against future cell loss.
Any mentally stimulating activity should help to build up your brain. Read, take courses, try "mental gymnastics," such as word puzzles or Soduku.  Experiment with things that require manual dexterity as well as mental effort, such as drawing, painting, and other crafts.

2. Get physical exercise
Research shows that using your muscles also helps your mind. Animals who exercise regularly increase the number of tiny blood vessels that bring oxygen-rich blood to the region of the brain that is responsible for thought. Exercise also spurs the development of new nerve cells and increases the connections between brain cells (synapses). This results in brains that are more efficient, plastic, and adaptive, which translates into better performance in aging animals. Exercise also lowers blood pressure, improves cholesterol levels, helps blood sugar balance and reduces mental stress, all of which can help your brain as well as your heart.

3. Improve your diet
Good nutrition can help your mind as well as your body. For example, people that eat a Mediterranean style diet that emphasizes fruits, vegetables, fish, nuts, unsaturated oils (olive oil) and plant sources of proteins are less likely to develop cognitive impairment and dementia.

4. Improve your blood pressure
High blood pressure in midlife increases the risk of cognitive decline in old age. Use lifestyle modification to keep your pressure as low as possible. Stay lean, exercise regularly, limit your alcohol to two drinks a day, reduce stress, and eat right.

5. Improve your blood sugar
Diabetes is an important risk factor for dementia. You can help prevent diabetes by eating right, exercising regularly, and staying lean. But if your blood sugar stays high, you'll need medication to achieve good control.
 
6. Improve your cholesterol
High levels of LDL ("bad") cholesterol are associated with an increased the risk of dementia. Diet, exercise, weight control, and avoiding tobacco will go a long way toward improving your cholesterol levels. But if you need more help, ask your doctor about medication.

7. Avoid tobacco
Avoid tobacco in all its forms.

8. Don't abuse alcohol
Excessive drinking is a major risk factor for dementia. If you choose to drink, limit yourself to two drinks a day.

9. Build social networks
Strong social ties have been associated with a lower risk of dementia, as well as lower blood pressure and longer life expectancy.

10. Care for your emotions
People who are anxious, depressed, sleep-deprived, or exhausted tend to score poorly on cognitive function tests. Poor scores don't necessarily predict an increased risk of cognitive decline in old age, but good mental health and restful sleep are certainly important goals.

 
Source: https://www.health.harvard.edu/mind-and-mood/12-ways-to-keep-your-brain-young