Dementia is the leading cause of dependence and disability. The number of people living with dementia worldwide is currently estimated at 47 million and is projected to increase to 75 million by 2030 and triple by 2050.

However, contrary to what some may think, dementia is a syndrome, not a normal part of aging.

Alzheimer's disease is the most common cause of dementia. Experts think between 60 percent and 80 percent of people with dementia have Alzheimer's, and an estimated 5.2 million Americans of all ages had Alzheimer’s in 2014.

This includes an estimated 5 million people age 65 and older and approximately 200,000 individuals under age 65 who have younger-onset Alzheimer’s.

Alzheimer's disease is thought to be caused by a combination of genetic, lifestyle and environmental factors that affect the brain over time.

A small percent of the time, less than 5 percent, Alzheimer's is caused by specific genetic changes that virtually guarantee a person will develop the disease. Although the causes of Alzheimer's aren't yet fully understood, its effect on the brain is clear — damage and death to brain cells, and eventually, significant brain shrinkage.

A new landmark study led by the University of East Anglia (UK) and funded by Alzheimer's Society, however, indicates that antidepressants and bladder medications may be linked to dementia.

Anticholinergics, which prevent acetylcholine from binding to muscarinic and nicotinic receptors and are prescribed in health conditions such as overactive bladder, seasonal allergies, and depression, might result in numerous adverse drug events, especially in older adults.

Anticholinergic antidepressants have been found to be linked with dementia, even when taken up to 20 years before a diagnosis. This research also noted a dementia risk associated with medications prescribed for bladder conditions and Parkinson's.

The researchers studied the medical records of 40,770 patients aged over 65 diagnosed with dementia and compared them to the records of 283,933 people without dementia, analyzing more than 27 million prescriptions.

The researchers noted that patients who had been diagnosed with dementia were up to 30 percent more likely to have been prescribed specific classes of anticholinergic medications. The researchers were unclear whether the medication was the cause or whether the medications had been prescribed for early symptoms that indicated dementia onset.

However, the researchers theorize that because the link goes back to 15 or 20 years before a diagnosis of dementia was made, treating early dementia symptoms was probably not the case. More likely, the explanation relates to the millions of people suffering from depression and 13 percent of men and 30 percent of women with bladder conditions in the United States and the United Kingdom, both disorders commonly treated with anticholinergic medications.

This is the largest and most detailed study exploring the long-term impact of anticholinergic use in relation to dementia.

According to Dr. Doug Brown, chief policy and research officer at Alzheimer's Society, the current guidelines recommend anticholinergic drugs be avoided for frail older patients because of their impact on memory and thinking but suggest that physicians should consider these new findings for all patients over age 65 as long-term use could raise the risk of dementia.