Diet, ExerCIse and carDiovascular hEalth (DECIDE) - Salt Reduction Strategies for the Elderly in Nursing Homes in China

The DECIDE - Salt in Elderly (Diet, ExerCIse and carDiovascular hEalth - Salt Reduction Strategies for the Elderly in Nursing Homes in China) is a study in the DECIDE project, which includes five studies. The others are DECIDE - Diet, DECIDE - Exercise, DECIDE - Obesity in Children, and DECIDE - Smart Living. The DECIDE - Salt in Elderly study is to evaluate the effects, safety and cost-effectiveness of salt substitution (SS) and kitchen-based stepwise salt supply control (SSSC) in reducing blood pressure in Chinese elderly in nursing homes. Specifically, the study aims include:

1. to test if a stepwise salt supply control strategy could significantly reduce systolic blood pressure among elderly living in nursing homes;
2. to test if replacing regular salt with the market available salt substitute could significantly reduce systolic blood pressure among elderly living in nursing homes; and
3. to test if the joint effect of the two strategies is larger than that from one of each.

The corresponding null hypotheses that will be tested are:

1. the mean change from the baseline in systolic blood pressure of elderly residents in nursing homes that are supplied with SS is equal to the mean change from the baseline in systolic blood pressure of elderly residents in nursing homes that are supplied with regular salt;
2. the mean change from the baseline in systolic blood pressure of elderly residents in nursing homes that apply SSSC is equal to the mean change from the baseline in systolic blood pressure of elderly residents in nursing homes that do not apply SSSC;
3. There is no interaction between the two interventions above.

The study will recruit over 960 old people from 48 nursing homes in northern China, where the mean salt intake is generally higher than 12 g/day. A 2x2 factorial cluster-randomized trial will be used to test two independent salt reduction strategies: 1) using salt substitute to replace the regular salt in the kitchen of nursing homes; and 2) training the nursing manager to control/reduce, step by step, the amount of salt supplied to the kitchen of nursing homes. The 48 nursing homes will be randomized to the following 4 groups.

1. salt substitute (SS) and stepwise salt supply control (SSSC);
2. SS only;
3. SSSC only; and
4. no SS and no SSSC (control).

A brief health education on salt and health will be applied to all four groups. The salt substitute (NaCl 62.5% and KCl 25%) will be centrally provided. And the Train-the-trainers model will be used to train the nursing home managers how to implement the SSSC.

The intervention will last over 2 years. The baseline examination including three blood pressure measurements and one 24-hr urine collection will be conducted for all participants. Fasting blood samples will be drawn for measurement of serum potassium and detect hyperkalemia, hypokalemia, hyponatremia and renal dysfunction.

The randomization will be conducted centrally by the study coordinating center at Peking University Clinical Research Institute, after the baseline survey completed.

All participants will be followed up for blood pressure measurements at 6, 12, 18 and 24 months, for serum potassium at 12 and 24 months, and for 24-hr urine collection at 24 months.

Study outcomes:

Primary outcome: The change in systolic blood pressure from baseline to follow-up.

Secondary outcomes: The incidence of hyponatremia, hyperkalemia, hypokalemia and renal dysfunction from the baseline to 24 months. The change in 24-hr urinary sodium, potassium and microalbumin from the baseline to 24 months. The change in diastolic blood pressure from baseline to follow-up. The incremental cost-effectiveness ratio (ICER). The incidence of cardiovascular events and all causes death during follow up.

Power analysis:

On the assumptions of a 20% dropout rate, an intraclass correlation of 0.02, the number of clusters of 48 and at least 20 elderly people in each nursing home, and an α value of 0.05, the study to detect a mean 3.0 mmHg reduction in systolic blood pressure (SD, 18 mm Hg) between the intervention groups would have a power of 0.81. To detect a 4.0 mmHg reduction in systolic blood pressure (SD, 18 mm Hg), the power of the same sample size would be 0.96.

Statistical analysis: Linear models adjusted for clustering based on participants with available measures were used to assess continuous outcomes. Frailty survival models that account for clustering based upon all randomised participants were used for analysis of the effects on cardiovascular and mortality outcomes. Generalized linear mixed model were used for analysis of effects on hyperkalemia, hypokalemia, hyponatremia and renal dysfunction..

Ethical considerations:

The study will be submitted to and approved by the Peking University IRB, which has the full accreditation from AAHRRP. The study salt substitute is the product available on Chinese market and has been approved manufactured according to the product standards issued by the ministry of health. The SSSC approach will take every step for 3 months and the biggest step of salt reduction will be just 10% of the original amount of use. And the study will ensure an interview will be conducted to collect the feedback before every next step will take place. The SSSC intervention will stop at any time that elderly people feel unlike the foods.