Intro

Ever been to the doctor and have them give you those 2 funky numbers?

That's called blood pressure honey.

Me and @Hussein Khambhalia spent around 2 hours on the weekend to see if we had the ability to calculate the cost effectiveness of something. That weekend we looked into potassium chloride fortification in the US.

Semi inspired by: Europe Should Require Foods Be Fortified With Folate 

Context

Nearly half of adults have high blood pressure (48.1%, 119.9 million). This is defined as a systolic blood pressure greater than 130 mmHg or a diastolic blood pressure greater than 80 mmHg or are taking medication for high blood pressure.^[1]

About 1 in 4 adults with high blood pressure has their blood pressure under control (22.5%, 27.0 million).^[1]

High blood pressure costs the United States about $131 billion each year, averaged over 12 years from 2003 to 2014.^[1]

In 2022, high blood pressure was a primary or contributing cause of 685,875 deaths in the United States.^[1]

Pulling it out from the data above:

Ischaemic heart disease (Coronary Heart Disease) - 2556.34 DALY rate per 100,000 population

Stroke: 1024.89 DALY rate per 100,000 population

Intervention

Potassium chloride can be used as a salt substitute for food, but due to its weak, bitter, unsalty flavor^[2], it is often mixed with ordinary table salt (sodium chloride) to improve the taste, to form low sodium salt. ^[3]

Every 10 mm Hg reduction in systolic blood pressure significantly reduced the risk ... coronary heart disease (0·83, 0·78-0·88), stroke (0·73, 0·68-0·77) ...^[4]

Calculations

Let's say we attempt to fortify the USA with potassium chloride.
$6\text{mmol/day}\approx 230\text{mg potassium}\approx 500\text{mg potassium chloride}.$

This corresponds to about a drop in Systolic Blood Pressure (SBP) of 1mmHg, which will reduce stroke and CAD risk.

Given that a slice of white bread has around 150mg sodium, it's not unreasonable that we could fortify people's food to hit 230mg a day.

Recall:

• Ischaemic heart disease (Coronary Heart Disease) - 2556.34 DALY rate per 100,000 population
• Stroke: 1024.89 DALY rate per 100,000 population

The US population in 2019 was 328.3 million.

Therefore, the total burden of CAD and Stroke in the US is around:
$\text{CAD}:\frac{2556.34}{100,000}\times 328,300,000=8,392,464\text{DALYs}$ 
$\text{Stroke}:\frac{1024.89}{100,000}\times 328,300,000=3,364,713\text{DALYs}$

Assuming a linear relationship of the disease risk factors. A drop of 1mmHg in SBP works to reduce the risk of the disease by:
$\text{CAD Risk}:1.7\%$
$\text{Stroke Risk}:2.7\%$

Thus, this intervention would net us:

$\text{CAD}:8,392,464\times 0.017=142,672$
$\text{Stroke}:3,364,713\times 0.027=90,847$

Total DALYs saved:
$142,672+90,847=233,519\text{DALYs}.$

Costs

Here is an estimate that suggests the cost of fortifying folic acid is linear ~ $1.5 million being the fixed cost. Cheaper than I expected. Thus we are assuming fixed costs are relatively trivial.

Estimates of annual fortification costs for the 140-mcg fortification strategy ($3.3 million) were based on those used by Grosse and colleagues, and those for the two hypothetical scenarios ($6.0 and $10.6 million for 350-mcg and 700-mcg fortification strategies, respectively)^[5]

Below we can see the cost of potassium chloride is about $300 a metric ton.

If we try to get 0.5g of potassium chloride to every American that would be about 164,150 metric tons. A naive calculation would give us $50 million as the material cost.

Canada produces at least 25 million tons a year (no idea how much of that is food grade). Which means that we aren't hitting a physical limit at least.

Because I have no idea on the price elasticity of potassium chloride, we will go from the $300 to up to 8x the cost for visualisation purpose. 

And the final results:

Given that most Western countries value a DALY in excess of $50,000,^[6] this seems like an interesting route to look more into?

Problems

I suspect there's a lot of problems, would love to hear your thoughts! Here is a non exhaustive list that I could think of:

• Palatability issues
• Potassium Chloride food grade manufacturing cost
• Potassium Chloride commodity price elasticity
• Adverse effects from those who are sensitive to potassium, i.e. hyperkalemia
• People who already have low blood pressure

But on the flipside there are things that could make potassium chloride fortification stronger:

• Marginal benefit of one less CAD/Stroke victim, i.e. their productivity or getting to spend the resources on their medical care elsewhere. $131 billion a year is a lot.
• Reduction in risks for not just Stroke, and CAD but all Cardiovascular diseases
• The intervention in another country being cheaper than the US

Conclusion

It was quite satisfying to synthesise a concrete number. LARPing as a bad GiveWell employee was overall pretty fun! I think we might continue + with any feedback.

I hope this inspires others to give it ago, maybe an attempt to recalculate our number more comprehensively or test out another intervention.

As an aside, I hope everyone checks their blood pressure and try to keep it at a healthy number, it's called the silent killer for a reason. Maybe you might try some potassium chloride ;)

1. ^{^}

   https://www.cdc.gov/high-blood-pressure/data-research/facts-stats/index.html

2. ^{^}

   It tastes pretty good to me lmao

3. ^{^}

   https://en.wikipedia.org/wiki/Potassium_chloride#Culinary_use

4. ^{^}

   https://pubmed.ncbi.nlm.nih.gov/26724178/

5. ^{^}

   https://pubmed.ncbi.nlm.nih.gov/18590584/

6. ^{^}

   https://www.givewell.org/how-we-work/our-criteria/cost-effectiveness/comparing-moral-weights