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Nulls: July-August 2021

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Here’s a very quick summary of some randomized controlled trials (RCTs) and meta-analyses of RCTs that were published in July or August of 2021 and didn’t find evidence of an effect. This is known as a null effect.

Keep the following in mind when interpreting a null effect:

  • While one study can provide evidence that something doesn’t work, it doesn’t prove it. Similar, repeatable results from multiple studies make for stronger evidence, whether the finding is positive or negative.

  • Not all null effects are the same. A meta-analysis of low-quality studies or a small clinical trial usually won’t provide strong evidence, whether the finding is positive or negative.

  • The population matters. For instance, the lack of an effect in healthy young people doesn’t necessarily mean that an intervention wouldn’t work in people who are older and have a specific health condition.


Circulating vitamin C levels may not be causally related to cancer risk[1]

What was studied? Researchers investigated whether plasma vitamin C levels were linked to the risk of developing breast, rectal, colon, prostate, lung, or bronchus cancer through a Mendelian randomization analysis.

Why study it? Several observational studies have found that higher circulating levels of vitamin C correlate with lower cancer risk. Randomized controlled trials looking at vitamin C supplementation have shown inconsistent results, possibly because of noisy data due to the low amount of cancer cases that occured of the course of the trials. Mendelian randomization can provide insight into whether higher vitamin C plasma levels are causally linked to cancer rates.

What was(n’t) found? There was no clear relationship between vitamin C levels and cancer risk at any of the five sites explored.

How null was it? Somewhat null. However, the study can’t directly speak to high-dose vitamin C supplementation since blood levels seen in the study weren’t that high, and the data also speak to longer-term exposure rather than the exposure profile seen under supplementation. Finally, the study wasn’t powerful enough to rule out small effect sizes.

Gut health

Vitamin D sublingual spray supplementation had no apparent effect on IBS symptom severity[2]

What was studied? This study was designed to evaluate whether 3,000 IU of vitamin D3 daily, delivered as a sublingual spray, affected symptom severity or quality of life in people with IBS and without obesity during winter. At baseline, around 60% of the participants were vitamin D insufficient or deficient. Their average baseline IBS symptom severity score (the primary outcome of the study) was about 280 out of 500, making the severity moderate on average.

Why study it? Studies previously examining the effects of vitamin D supplementation on IBS symptoms have been positive, but had a few drawbacks. They either used bolus dosing, which may present safety concerns, or were short in duration. Plus, many of them had pretty small sample sizes. The study may have also been conducted in order to test a commercially available vitamin D spray, since the company that manufactures it (BetterYou) partially funded the study and provided materials to the researchers.

What was(n’t) found? The spray was effective at raising vitamin D blood levels, with bigger boosts seen in people with lower starting levels. However, there was no effect on either IBS symptom severity score or quality of life. There was also no correlation between change in vitamin D levels and symptom score.

How null was it? Pretty null, with some caveats. The researchers attempted to recruit enough people to detect a roughly 40-point difference symptom severity score between the placebo and supplement groups. However, they were unable to recruit the amount of people needed. Also, the placebo effect the authors observed in this study was much stronger than that seen in the pilot study. Both of these factors leave a little room for doubt, although the data don’t even hint at an effect existing. Also, this null result only speaks to low daily dosing via sublingual spray. Other previous trials have found an effect, but they all used high or bolus dosing, all focused on Middle Eastern populations, and some of the studies may have had some methodological limitations.

Anything else? These authors deserve praise because their study is a great example of how industry-funded supplement studies should ideally be written and reported. Even though the main results were null, the study was well designed and relevant. The researchers presented complete analytic procedures and statistics, plus exploratory analyses were clearly labelled as such, with relatively little spin.

Healthy aging & longevity

Leucine, creatine, or protein supplementation didn’t provide much additional benefit on top of resistance training for older people with frailty or pre-frailty[3]

What was studied? Researchers evaluated whether 7.5 grams of leucine, or 30 grams of soy or whey protein with or without 6 grams of creatine daily improved muscle function and lean mass when added to a twice-weekly progressive full-body resistance training program for 16 weeks. The participants were over 65 years old and consisted mostly of women. The participants were classified as either pre-frail or frail using a five-domain scoring system. The population that wound up being recruited wound up being mostly pre-frail rather than frail.

Why study it? Muscle loss is a major factor in frailty, which itself is associated with several poor outcomes as people age. Boosting muscle function and muscle mass by adding supplements to resistance training could potentially help stave off frailty and the negative effects that come with it as people age.

What was(n’t) found? While the resistance training program was effective at improving muscle function (measured by several things, ranging from everything from one-repetition max bench presses to timed standing tests) and lean mass (measured by DXA), there was no clear added benefit for any of the supplementation regimens.

How null was it? This study measured a lot of variables and had a pretty small sample size: each group had just over 20 participants. Also, compliance for supplement taking was less than ideal. This opens the possibility that future research could uncover effects that this study might have missed.

Anything else? The study design was pretty complex, involving several groups and comparisons are not fully fleshed out here. Also, one key takeaway is that there was no report of adverse effects or exercise injuries, which provides some evidence that the exercise regimen used in this study could be safe and effective in a mostly pre-frail population.

Infants, children & teenagers

Raising fruit and veggie intake didn’t help children’s asthma exacerbations[4]

What was studied? In this study, researchers evaluated whether raising fruit and vegetable intake by around 3.5 servings per day in children ages 3–11 with recent asthma exacerbations had any effect on future exacerbations or lung function.

Why study it? Mechanistically, oxidative stress is elevated in the context of asthma, and since fruit and vegetables could lower oxidative stress and inflammation, increasing intake could affect asthma. Also, a randomized controlled trial in adults run by the same group found that people randomized to a low fruit and vegetable intake group were at an increased risk of asthma exacerbation compared to people randomized to a high-intake group.

What was(n’t) found? There was no clear difference in the primary outcome of time to first asthma exacerbation between the high-intake and control groups. There was also no clear effect on exacerbation rate.

How null was it? The study was powered to detect a pretty large effect size (hazard ratio of 2.3) for the primary outcome of time to first asthma exacerbation, which was based on a similar study in adults. Thus, the study can’t rule out smaller but still clinically significant differences.

Anything else? When the authors looked only at children in the high-intake group who adhered well to the study protocol, they found an improvement in one aspect related to breathing function (airway reactance), which may suggest future research could be useful.

Ketone salts and whole-body cooling didn’t effectively improve short-term performance[5]

What was studied? The authors investigated whether ketone salts with or without whole-body cooling could affect cycling time trial performance in young, aerobically fit men who were not endurance-trained. The ketone supplement was taken 30 minutes prior to the exercise, and dosed at 0.3 grams of 50/50 racemic mixture of R/L β-hydroxybutyrate per kg of body weight, providing 0.01 g/kg of sodium and potassium. In the cooling plus ketone supplementation conditions, participants sat in a 0° C room with a vest fitted with ice packs for 30 minutes.

Why study it? Ketone salt supplementation and whole-body cooling have both been found to improve aerobic performance in the past, but whether their combination could boost performance synergistically hasn’t been tested before.

What was(n’t) found? There was no clear improvement in time trial performance in either the ketone or ketone plus whole-body cooling conditions.

How null was it? Not very, for at least two reasons. The first was that the study was only powered to detect large effect sizes, and so could have missed medium, but still practically significant, effect sizes. Also, the study design didn’t include a familiarization phase, which may have added more noise to the results, since the participants may not have had much experience with time trials, given that they weren’t participating in endurance training.

Muscle gain & exercise

Ammonia inhalants increase arousal but not necessarily performance [6]

What was studied? This study was designed to determine whether inhaling sharply from a flask containing ammonium carbonate improved measures of neuromuscular performance in healthy non-resistance-trained young men. Inhalation was done no more than 30 seconds before performance measurements after a warm-up for each of the metrics.

Why study it? Surveys of athletes, especially powerlifters, have found that many of them use ammonia inhalants to raise alertness and improve performance. However, the efficacy of this technique remains mixed, with one study finding that peak power improved in already-fatigued athletes, but other studies finding little effect. Some researchers have suggested that non-resistance trained athletes may benefit more from ammonia-induced arousal, but this hypothesis hasn’t been tested before.

What was(n’t) found? Ammonia inhalants reliably boosted heart rate, alertness, and the participants’ self-evaluation of how well they performed in the trials. However, there was no clear improvement in any of the three performance measures tested (hand grip and knee extension maximal voluntary contractions, or peak power during countermovement jumps).

How null was it? No power calculation was performed, so it’s not clear if these results could have been false negatives. The sample size was 14 participants, but the study was conducted as a cross-over trial. Based on quick calculations by the Examine editors, this study may have had the power to detect a medium to large effect.

Adding whey protein concentrate or hydrolysate to suboptimal carb intake didn’t impact 24-hour recovery in trained cyclists[7]

What was studied? The authors of this study investigated whether adding 0.3 g/kg body weight of either whey protein concentrate or hydrolysate to a post-exercise drink containing suboptimal amounts of carbohydrate (1.2 g/kg body weight — about half the needed dose) could help with next-day performance after a two-hour exercise bout in trained male cyclists. The initial exercise bout was designed to mostly, but not completely, deplete the athletes’ glycogen stores. Total energy intake was matched between conditions.

Why study it? Previous research has established that a sufficient amount of carbohydrates post-exercise can aid in endurance athletes’ recovery and boost future short-term performance after an intense exercise bout. However, a lot of athletes’ habitual carbohydrate intake doesn’t meet their carbohydrate requirements. Other research has suggested that adding some protein to post-exercise carbohydrates could help replenish glycogen stores more effectively by boosting glucose uptake via insulin-independent and -dependent routes. However, this research has mostly focused on short-term effects under eight hours. A more realistic test focused on next-day performance hasn’t been conducted. It’s also unclear whether intact protein or hydrolysates could be more effective for this purpose.

What was(n’t) found? Next-day 30 minute time-trial performance was not different between carbohydrate-only and either protein conditions, even though insulin responses were higher in both protein conditions. Ratings of perceived exertion weren’t different, either. Carbohydrate oxidation was lower on the second day than on the first under all conditions, suggesting that glycogen was not completely restored in any of the conditions.

How null was it? On one hand, this trial was designed to more closely mimic conditions more relevant to training athletes by measuring next-day performance using suboptimal carbohydrate amounts after undergoing rigorous, but not completely exhaustive, training. In that sense, it’s a bit more null than other experiments looking at shorter time frames. On the other hand, the study was powered to detect a large effect size and would have trouble distinguishing medium or small effects. Also, it does not rule out stronger cumulative effects over the longer haul, since it still only tested next-day performance. It also does not rule out benefits after completely exhaustive exercise. Indeed, one trial[8] that found benefits from adding protein to carbs using a more exhaustive time-to-exhaustion test, which bolsters this hypothesis.

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See other articles with similar topics: Nulls.

See other articles in Issue #83 (September 2021) of Study Deep Dives.

Other Articles in Issue #83 (September 2021)