Hypertension Flashcards
What is hypertension?
Blood pressue: force blood exerts against arterial wall; expressed in mmHg systolic/diastolic
* <120/<80 = normal blood pressure
* ≥140/≥90 = hypertension
Mechanics of Blood Pressure
Blood pressure is directly related to blood volume
* Blood pressure is increased when
resistance to blood flow is increased
* Lumen of vessel is decreased
* Length blood must travel is increased
* Viscosity of blood is increased
What controls the blood pressue (BP)?
Nervous system control
Endocrine control
How does the nervous system controls blood pressure?
- BP regulated by cardiovascular center in medulla oblongata
- Receives input from baroreceptors
- Regulates heart rate & force of contraction, vessel dilation/constriction
How does the endocrine system controls blood pressure?
Renin-angiotensin-aldosterone system (RAAS) - inc. bp
Epinephrine & norepinephrine - inc. bp
Antidiuretic hormone (vasopressin) - inc. bp
Atrial natriuretic peptide - dec. bp
Renin-Angiotensin-Aldosterone System (RAAS)
**Renin **released in response to:
* Low BP, low extracellular fluid (ECF) volume, low plasma Na
Aldosterone stimulates
* Na + reabsorption→ increases
extracellular fluid osmolality → promotes fluid retention → rise in BP
Characterisitics of hypertensin
- Usually no signs or symptoms
- Tends to rise with age
- Commonly co-exists with type 2 diabetes, obesity
- Overtime, damages blood vessels, heart, kidneys..
- Risk factor for heart disease, aneurysm, stroke and
kidney failure
Evidence of hypertension in Canada
- Hypertension has been cited as the most common reason for doctor’s visits & most common reason for taking medications
- 2018 - 25% of Canadian adults >20 years live with diagnosed hypertension
- Approximately 20% of individuals with hypertension are not aware of their condition, the true prevalence of hypertension is likely higher
Diet & Hypertension
- “Dietary changes can serve as first-line therapy, before antihypertensive medication, for treating
uncomplicated hypertension. - Among hypertensive individuals who are already taking medication, dietary changes can further
lower BP and make it possible to reduce the number and dose of antihypertensive medications.” - genetics can not be changed through dietary changes
How is body weight related to hypertension?
For each extra pound of body fat, an
estimated 400 miles of additional
blood vessels develop
- longer distance - inc. pressue
Role of Sodium (Na+) in hypertension
- Main cation in extracellular fluid
- Role in maintenance of fluid homeostasis – balance of extracellular (ECF) and
intracellular fluids (ICF) - More Na+ in blood = increased osmolality, pulls more water
into blood → increases bp - Key regulator of blood volume and blood pressure
- Na conserved by renin-angiotensin
aldosterone system & excreted with increases atrial natriuretic peptide
Multiple studies (animal, observational and experimental) have shown a direct relationship between dietary sodium and hypertensioon
Recommendation of salt intake
- Suggests **3 g salt/day **(about 1.2 g sodium/d) as population target intake
Note: AI for adults 9-50 yrs: 1500 mg/day
UL for adults 14-50 yrs: 2300 mg/day
Sodium vs Salt
- ~ 90% of dietary sodium comes from sodium chloride or “salt”
- Salt is about 40% sodium by weight
Approximate equivalents - 1/4 teaspoon salt = 575 mg sodium
- 1/2 teaspoon salt = 1,150 mg sodium
- 3/4 teaspoon salt = 1,725 mg sodium
- 1 teaspoon salt = 2,300 mg sodium
High Sodium Intakes
- 85 % of men & 60-80% of women aged 9-70 exceeded the UL for sodium intake
- Men 19–30 years had highest median sodium intake: 4046 mg/day
Sodium in Canadian Diets
77% Processed Foods
12% Naturally occuring in foods
6% Salt added at table
5% Salt added during cooking
Is a population-wide decrease in sodium intake needed?
- Sodium may increase blood pressure, which is a known risk factor for CVD
- It has been estimated that if the Canadian average sodium intake is decreased by ~1800
mg /day - high blood pressure prevalence would dec. by 30%.
- benefit of reducing salt at inidividual level
- some studies show no effect or even inc. risk for death due ti cardiovascular disease among those with lower sodium intakes
How can individual response to dietary sodium varies?
Individual response to dietary sodium reduction lies somewhere along the continuum
“Salt Resistant”
- bp does not respond considerably to changing sodium intake
**“Salt Sensitive” **
- bp responds greatly to decrease in sodium intake
Sodium “response” depends on
- current blood pressue
- age
- race
- potassium intake
- renin-angiotinsin-aldosterone system
What are the possible limitations of studies on sodium & CVD?
- Observational studies – cannot show causation
- Small sample size, few cases of CVD
- Reverse causation - Individuals at risk (or diagnosed with) a disease may change their
diet/lifestyle as a result of medical advice or to prevent recurrence
or complications from occurring - Errors in estimating sodium intake
- Short term studies underestimate the effect of
sodium reduction on blood pressure
How to estimate sodium intake?
- Dietary estimates (Dietary recalls/records, FFQ)
- Urinary sodium excretion
- Approximates dietary intake
- Urinary collection at one time point or over 24 hrs
What are sources of error in urinary excretion?
- Medical condition
- Incomplete collection
- Hydration
- High participant burden (may lead to drop-outs)
- Differences in losses in sweat & feces
- Lab error
- Day to day variation
- Modifying intake because know being measured
What are sources of error dietary sodium?
- Over/underestimate portion sizes
- Missed addition of salt/condiments at table
- Differences in sodium content of similar foods
- Accurate database for sodium content of foods
- Single recall may not be representative of usual
intakes
What is the source of error for one time 24-hr urinary collection?
ONE 24-hr urinary collection or dietary recall may not be representative of usual intake due to INTRA-individual variation in sodium intake
Evidence: O’Donnell MJ et al. Salt intake and cardiovascular disease: why are the data inconsistent?
- Method of measuring sodium
- Effects may differ by geographical region, depend on range of sodium intakes
- “Salt sensitivity” of individuals
- Influence of other dietary factors
- Sodium -> BP -> CVD may be too simplistic
Bottome line:
- high dietary sodium intake (>5 g/d) associated with increased CVD risk
- moderate sodium intake may or may not be associated with increased CVD risk
- more research is needed to understand relationship between sodium and CVD and whether there is a safe lower threshold of sodium intake
Role of Potassium in hypertension
- Major intracellular cation
- Higher intakes associated with lower bp
- Has opposing effects from Na + on fluid and bp regulation
- Interaction between K+ and Na + on bp
- Eg. Effects of K+ are greatest when Na + intake is also high
- Best source is fruits and vegetables
Dietary Approaches to Stop Hypertension: The DASH diet
- Emphasizes vegetables, fruits, and fat-free or low-fat dairy products
- Includes whole grains, fish, poultry, beans, seeds, nuts, and vegetable oils
- Limits sodium, sweets, sugary beverages, and red meats
- Consistent with dietary habits associated with reduced risk for chronic conditions such as cancer,
heart disease, osteoporosis, etc.
The DASH diet: Dietary components
Saturated fat: 6% of kcal
Sodium: 2300 mg (1500 mg better)
Potassium: 4700 mg
Calcium: 1250 mg
Magnesium: 500 mg
Fibre: 30 g
What are the main dietary factors affecting hypertension and clinical recommendations?
Body weight (increased visceral fat)
- for overweight and obese subjects, lose weight
- for lean individuals, maintain normal weight (optimal BMI < 25 kg/m^2)
Salt
- as low intake as possible
- ideally less than 3.8 g/d (corresponsing to 65 mmol or 1.5 g of sodium per day)
Potassium
- not less then 120 mmol or 4.7 g per day
Alcohol
- for mean, < or equal 2 drinks/day
- for women, < or equal 1 drinks/day
- the safest level: ZERO
DASH-type dietary pattern
- diet rich fruits, vegs, and low-fat dariy porducts and low in saturated fat
