Scientists use cross-sectional studies and case-control studies to identify risk factors that may contribute to a disease, like smoking, low sunlight or low vitamin D. Cross-sectional studies are what they sound like: a cross-section of a population at a moment in time. Usually they are designed like cohort studies, where there is a known measurement in an entire population (like sun-exposure) and the researchers then look at disease outcomes.
Case-control studies are a little different in that they compare subjects who already have a condition or disease (the ‘cases’) with subjects who do not have the condition but are otherwise similar (the ‘controls’). One triumph of case control studies was the study on smoking and lung cancer by Sir Richard Doll. Doll’s detractors argued for many years that this type of study cannot prove causation, but Doll’s work held true, and we now accept that smoking causes many deaths from lung cancer.
The last and highest step is a randomized human controlled trial, where scientists subject half of the subjects to placebo and half to vitamin D (or smoking) and see what happens. How many randomized controlled trials do we have on vitamin D? Probably a little over one hundred? How many randomized controlled trials do we have on smoking? None. One cannot randomize half the patients to smoking; it’s unethical.
However, science says we must wait some more on vitamin D, that statistical problems make these discoveries unreliable. Sir Richard Doll lived to see his smoking discovery verified. However, Professor Cedric Garland at UCSD is still waiting.
In 1980, he and his brother Frank discovered that vitamin D helps prevent colon cancer using a cross-sectional study design. You can still die from colon cancer if you go into the sun but your risk is less. Their critics said the Garlands must wait for more studies.
Frank Garland died waiting. I hope we recognize Cedric Garland for his exceptional discoveries before his time comes. One thing you could do to help is recognize Professor Garland’s contribution. Just email him a few words at email@example.com and say thanks for all he has done for humanity.
Let’s also not forget, he and his colleagues discovered the same thing about breast cancer.