The Newcastle 85+ Study is a prospective cohort of people born in 1921 in Newcastle upon Tyne and North Tyneside (North East England) (20). Participants were recruited in 2006-07 irrespective of their health state (except for terminal illness), living at home or in an institution. The TOOTH study is an observational cohort that randomly recruited people aged ³85 years resident in Tokyo (Japan) in 2008 (21). Both studies conducted multidimensional health assessments on a range of biological and social factors associated with health and functioning. Data collection was carried out by trained research nurses (Newcastle 85+), and trained interviewers, dentists and geriatricians (TOOTH) in participants’ homes and/or during clinic visits (TOOTH). The Newcastle 85+ Study collected information on health conditions and medication use from general practice record reviews (GPRR). The Newcastle 85+ Study followed the Code of Ethics of the World Medical Association (Declaration of Helsinki). Newcastle & North Tyneside Local Research Ethics Committee 1 approved the Newcastle 85+ Study. The Keio University School of Medicine (N0.20070047, Dec 2007) and Nihon University School of Dentistry (No.2003-20, 2008) approved the TOOTH study. TOOTH is registered in the University Hospital Medical Information Network Clinical Trial Registry (ID UMIN000001842). Able participants provided informed consent, with signed consultee approval from those participants lacking capacity. Participants from the baseline surveys (Newcastle 85+ Study n=853; TOOTH study n=542) were included in the present analysis.
Frailty, physical function, and mobility limitation
Participants underwent a physical examination at baseline when recruited into the studies. Frailty status was based on the Fried Frailty Phenotype (22) using data from questionnaires and physical assessments. Participants were coded as “frail” if meeting at least three of the five criteria of the Fried Frailty Phenotype Score (FFS); which included, in the Newcastle 85+ Study, unintentional weight loss, poor energy/endurance (self-reported question “do you feel full of energy"), low physical activity, weakness (grip strength), and slow gait speed (Timed-up-and-go or TUG test) (23). The same criteria were applied in the TOOTH study, except for poor energy/endurance which was based on the question “I have felt active and vigorous” (WHO-5 Well-being Index) (24).
Grip strength (GS) was assessed twice for each hand, alternating between hands, following a standardised protocol (25) using a Takei A5401 digital 0e100 kg x 0.1 kd LCD hand-held dynamometer. The TOOTH study used two measurements of grip strength of the dominant hand using a Tanita 6103 handheld dynamometer (Tanita cooperation, Tokyo, Japan). Walking speed was based on the TUG test using previously described methods to measure time taken to walk three meters (21, 23). Participants in both studies were classified as having mobility limitations if they reported difficulty getting around in the house, or going up and down stairs/steps, or walking at least 400 yards.
Oral health markers
The Newcastle 85+ study included a count of number of natural teeth as part of the physical examination of participants conducted by trained research nurses, as well as a question on the age at which the last remaining natural tooth was lost. Other oral health measures assessed through self-report questionnaires included dry mouth symptoms, difficulty swallowing, and difficulty eating foods because of problems with teeth or the mouth. Questions on dryness of mouth included sipping water through the night, taking liquids to help swallow dry foods, feelings of dry mouth when eating, and difficulty swallowing foods because of dry mouth. Report to any one of these questions was taken as presence of dry mouth symptoms. Difficulty swallowing was assessed through questions on difficulty swallowing foods due to dryness of mouth or any other reason, or difficulty swallowing liquids. Ten food items were listed to assess difficulty eating because of problems with teeth and mouth: crusty bread, toast, tomato, raw carrots, roast potato, cooked green vegetables, lettuce, well-done steak, apples and nuts. Responses included “eat easily”, “with some difficulty”, “could not eat at all”.
In the TOOTH study, a count of natural teeth was conducted by a dentist as part of the physical examination. Dryness of mouth was based on measures of salivary volume. Saliva was collected by spiting method for 3 minutes (26). Subjective measures of oral health included difficulties swallowing (“How often are you able to swallow comfortably”) (27) and chewing ability. Chewing ability was assessed from the ability to eat 15 foods differing in texture and hardness (easy to eat, eaten with effort, or impossible to eat): boiled rice, udon noodles, tuna sashimi, bananas, and boiled spinach (soft and easy to chew), roasted rice cake, sliced cabbage, hamburger, pickled Chinese cabbage, and rolled boiled fish (slightly difficult to chew), and hard rice crackers, peanuts, yellow pickled radish, boiled bamboo shoots, and pork cutlets (hard and difficult to eat).
Covariates
Socioeconomic position was based on UK Office for National Statistics Socio-economic Classification (Newcastle 85+ Study) or number of years of education (TOOTH study). Information on smoking and alcohol intake was collected as part of the study interviews and have been previously described (21, 28). Information on health conditions in the Newcastle 85+ Study from GPRRs included history of cardiovascular disease, diabetes, Alzheimer’s disease, Parkinson’s disease, hypertension, arthritis, osteoporosis, stroke, transient ischaemic attack, respiratory disease, and cancer in the last 5 years. Information on these co-morbidities was collected in the TOOTH study as part of the interview by experienced geriatricians (21). Cardiovascular disease (CVD) included stroke, transient ischaemic attack (TIA), myocardial infarction, and angina. Hypertension was defined as current use of medication for hypertension, self-reported diagnosis, or systolic blood pressure higher than 140 mmHg at baseline examination. Diabetes was defined as fulfilling one or more criteria: self-reported diagnosis, administration of insulin or other oral hypoglycemic medications, random plasma glucose ≥200 mg/dL, or hemoglobin A1c ≥6.5 %. In the Newcastle 85+ Study, GPRR records were used to ascertain regular use of prescribed medications with xerostomia (dry mouth) side effects. These medications were derived and classified using the British National Formulary (BNF https://bnf.nice.org.uk). The medications included antimuscarinics (anticholinergics), antidepressants (selective serotonin reuptake inhibitors, tricyclics), antihistamines, alpha-blockers, antipsychotics, skeletal muscle relaxants (baclofen, tizanidine), centrally acting anti-hypertensives (clonidine), opioids, and diuretics (thiazides and related diuretics, potassium sparing diuretics, etc.). Information on depression was obtained through the Geriatric Depression Scale (GDS-15) in the Newcastle 85+ Study, and through the WHO-5 Well-being Index (24) in the TOOTH study.
Statistical analyses
Responses to questions on difficulty eating because of dental problems in the Newcastle 85+ Study were coded as: “severe difficulty eating” (³3 of the 10 foods items as ‘could not eat at all’) and “Any trouble eating hard foods” (≥3 hard foods “with some difficulty” or “could not eat at all”). Number of teeth was grouped as having at least 21 teeth (29), number of remaining natural teeth (“none”, “1 to 7”, “8 to 14”, “15 to 20,” and “≥21”), and complete tooth loss (edentulism). In the TOOTH study, number of teeth was categorised as complete tooth loss, <21 teeth, and a three-category variable (0, 1-20, and ≥21 teeth); the three category variable best reflected the distribution of tooth loss in the TOOTH Study. Dry mouth was based on the lowest tertile of salivary volume (0.83g). Difficulty eating was categorised as “severe difficulty eating” (≥4 foods “impossible to eat”). “Any trouble eating hard foods” (≥2 hard foods “eaten with effort” or “impossible to eat”)
Slow walking speed was defined as values in the highest tertile of the TUG distribution (Newcastle 85+ Sudy, men: ≥15 seconds, women: ≥19 seconds; TOOTH study, men: ≥14.2 seconds, women: ≥16 seconds); and low muscle strength as values in the lowest tertile of the grip strength distribution (Newcastle 85+ Study, men: ≤23kg, women: ≤13kg; TOOTH study, men: ≤23kg, women: 14.3kg).
The relationship of oral health markers with frailty, mobility limitations, grip strength, and gait speed was assessed using logistic regression. Models for dry mouth were specifically adjusted for medications with xerostomia as a side effect (Newcastle 85+ Study) and depression (both studies).