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The products we choose for our store are carefully selected based on which supplements have the strongest evidence of benefit for various population groups. You can explore the "why we recommend" section within "view product" to see that evidence. As we find positive evidence for different use cases, we add to this list.
To assess vitamin D benefits, we compared results from multiple systematic reviews that review the literature.1,2,3,4,5
One of the most compelling drivers for our recommendation comes from the health society guidelines. For those over the age of 50, 6 of 8 health society guidelines recommend vitamin D.3 For adults of all ages, 4 of 7 guidelines recommend vitamin D for the general population (See research benefits below).3
Additionally for vitamin D:
Bone health and immunity are important parts of health, but a reduction in mortality is always quite interesting. In this case, the reduced mortality really highlights how important immunity and bone health are. First, improved immunity can reduce death from infectious diseases. Second, when the elderly break bones, it tends to accelerate age-related diseases because you can't move around for a few months. We can't say for sure what caused the reduced mortality in these 12 systematic reviews, but a stronger immune system and stronger bones can have a big impact.
To conclude, according to the US dietary guidelines, 90% of US adults are below the recommended vitamin D levels.6 Thus, if you do not get enough sun, your bones will benefit from vitamin D supplementation, and you might get immunity benefits too. Dive into the research, below!
8 out of 12 systematic reviews showed a reduction in mortality from vitamin D Supplementation (Rejnmark, 2017). The US preventive services task force did not find a statistically significant reduction when combining across their studies.
...
Sources: US Preventive Services Task Force, 2018 (1), Rejnmark, 2017 (2).
Combined data from 9 trials showed a statistically significant reduction in any fracture among elderly that took calcium and vitamin d supplements vs placebo (Avenell, 2014).
Across the studies reviewed by this cochrane review, there was a small, 2.6% improvement for bone mineral content in vitamin D deficient children (Winzenburg, 2010).
...
Sources: Avenell, 2014 (4); Winzenburg, 2010 (5).
3 of 7 meta analyses of trials have shown vitamin D may reduce the risk of respiratory infection.
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Source: Rejnmark, 2017 (2).
2 of 3 large trials and 2 of 3 cohort studies showed an increased risk of kidney stones with 7 years of vitamin D use, especially above 1000 IU / day or more.
...
Source: US Preventive Services Task Force, 2018 (1).
To assess vitamin D and calcium benefits, we compared results from multiple systematic reviews that assess the literature.1,2,3,4,5
One of the most compelling drivers for our recommendation comes from clinical guidelines from leading health societies around the world. For those over the age of 50, 6 of 8 health society guidelines recommend vitamin D, and 5 of 6 recommend calcium.3 For adults of all ages, 4 of 7 guidelines recommend vitamin D for the general population (See research benefits below).3 In other words, most adults benefit from vitamin D, especially the elderly who should also take calcium.
Additionally:
Bone health and immunity are important parts of health, but a reduction in mortality is always quite interesting. In this case, the reduced mortality really highlights how important immunity and bone health are. First, improved immunity can reduce death from infectious diseases. Second, when the elderly break bones, it tends to accelerate age-related diseases because you can't move around for a few months. We can't say for sure what caused the reduced mortality in these 12 systematic reviews, but a stronger immune system and stronger bones can have a positive impact.
To conclude, according to the US dietary guidelines, 90% of US adults are below the recommended vitamin D levels, and 30% and 60% of adult men and women, respectively, are below the recommended calcium intake.6 Thus, if you do not get enough sun, your bones will benefit from vitamin D and calcium supplementation, and you might get immunity benefits too. Dive into the research, below.
5 of 6 developed nation guideliens recommend calcium for the elderly, according to a review by Dai, 2021.
…
Sources: Dai, 2021 (3).
In a JAMA-published systematic review of the literature, daily supplementation with calcium and vitamin D resulted in a 17% reduction in hip fractures and an 8% reduction in all fractures, using data from 6 randomized trials.
Another systematic review also found a statistical association for calcium supplementation alone, across 20 studies. However results were inconsistent; potentially owing to the fact that vitamin d aids in calcium absorption (10).
Sources: Yao, 2019 (9). Bolland, 2015 (10).
3 of 7 meta analyses of trials have shown vitamin D may reduce the risk of respiratory infection.
...
Source: Rejnmark, 2017 (2).
Source: US Preventive Services Task Force, 2018 (1).
To evaluate the benefits of dietary fiber and psyllium, we compared results from multiple systematic reviews that assess the literature.1,2,3
Combined data from 23 studies showed a statistically significant reduction in total cholesterol and LDL cholesterol.1 In addition, combined data from 10 studies showed a statistically significant reduction in diastolic blood pressure.1
Psyllium is one such fiber supplement that has been tested for impact on heart health. Another review by Jovanovsky tested psyllium supplementation on heart health indicators and found reductions in LDL cholesterol, non-HDL cholesterol, and the apoB biomarker (using combined data from 28 studies).2
We recommend fiber to anyone who gets less than the recommended 25g of fiber per day, because it has well-supported heart health benefits and according to the National Health and Nutrition Survey, 90% of Americans don't get enough of it. Taking this fiber supplement will help increase your fiber intake, but you'll still need to eat your salads, veggies, and legumes!
Combined data from 23 studies showed a statistically significant reduction in total cholesterol and LDL cholesterol. This review leverages the larger sample size to draw this statistically significant outcome. Most of the studies trended in favor of reduced cholesterol, and 5 of the individual studies found a statistically significant reduction in total cholesterol.
Combined data from 10 studies showed a statistically significant reduction in diastolic blood pressure
Other improvements were seen in other cardiovascular biomarkers across studies, such as apoβ
Another review by Jovanovsky combined data from 28 studies of psyllium supplementation and found statistically significant reductions in LDL cholesterol, non-HDL cholesterol, and the apoβ biomarker
Sources: Hartley, 2016 (1) Jovanovsky, 2018 (2)
Adverse events were reported in 2 of 3 studies reviewed, including feeling full, feeling bloated, and having increased bowel movement frequency.
Source: Wharton, 2020 (3)
To assess magnesium benefits, we compared results from multiple systematic reviews that review the literature.1,2,3,4
While magnesium showed no impact on mortality or cancer risk,1 the combined data from 23 trials found a reduction in blood pressure.4 In addition, 4 out of 8 studies found a positive impact on anxiety for adults with mild anxiety.3 Meanwhile, 2 of 5 studies found benefits for sleep (including duration), but this finding was not seen in the majority of studies.2
In addition, 58% of Americans get less than the recommended amount of Magnesium, according to the National Health and Nutrition Examination Survey.
Combined data from 23 trials showed a small but significant reduction in blood pressure; Kass, 2012 (22).
4 of 8 randomized trials in mildly anxious adults showed a decrease in subjective anxiety scores.
4 of 7 studies on premenstrual syndrome anxiety found a decrease in subjective anxiety.
Source: Boyle, 2017 (21).
An Iranian review with good study aggregation methods found that 2 of 5 studies found improvement in some aspect of sleep (slow wave sleep time, total sleep time, etc.).
Source: Arab, 2022. (20).
Source: US Preventive Services Task Force, 2018 (11).
To assess fish oil benefits, we compared results from multiple systematic reviews that review the literature.1,2
The main benefit that is backed in the literature is that for improved heart health. In fact, fish oil is commonly recommended because four early, large randomized trials showed cardioprotective benefits of omega-3 fatty acid supplementation.1 Interestingly, since 2010, more recent trials have failed to replicate results. This may be due to improved cardiovascular treatment, increased fish consumption, or dose differences in the study designs.1 That being said, a recent meta-analysis (Zhang, 2022) published in the Journal of the American Heart Association showed that across 71 trials, increasing dosages of EPA and DHA omega-3 fatty acids resulted in larger decreases in blood pressure.3
Overall, fish oil might reduce the risk of cardiovascular disease, as there is still inconsistency in the data. The American Heart Association recommends 2 servings of fish per week as part of a healthy diet. It recommends about 3 g per day of DHA/EPA for those at high risk of cardiovascular disease, and suggests that more research is needed.4 If your fish intake is low, we recommend supplementing with this essential fatty acid.
Four early, large randomized trials show cardioprotective benefits of omega-3 fatty acid supplementation, but more recent trials have failed to replicate results, according to a systematic review published by Goel in 2018. This may be due to improved cardiovascular treatment, increased fish consumption, or dose differences in the study designs.
Another recent meta-analysis (Zhang, 2022) published in the Journal of the American Heart Association showed that across 71 trials, increasing dosages of EPA and DHA omega-3 fatty acids resulted in larger decreases in blood pressure.
Overall, fish oil might reduce the risk of cardiovascular disease, as there is still inconsistency in the data. The American Heart Association recommends 2 servings of fish per week as part of a healthy diet. It recommends about 3 g per day of DHA/EPA for those at high risk of cardiovascular disease, and suggests that more research is needed.
Source: Goel, 2018 (1). Zhang, 2022 (3). American Heart Association, 2022 (4).
Source: Sydenham, 2012 (2).
Folic acid supplementation, especially during the first month of pregnancy leads to a drastic reduction in neural tube defects.
A systematic review by de Regil found that across 5 studies involving 6708 births, folate or folic acid supplementation resulted in drastically lower rates of neural tube defects.1
Unfortunately, the benefits of folate or folic acid are most important during the first month of pregnancies. Often it takes a month or longer before learning that you are pregnant (50% of pregnancies are unplanned). As a result, the US Preventive Services Task Force recommends folic acid supplementation (400-800 mcg) for women who might bear a child, and supplementation should continue from 1 month prior to pregnancy through the 2nd or 3rd month of pregnancy.2
Drastic reduction in neural tube defects. Not enough information for other defects.
Source: De Regil, 2015 (1).
Source: US Preventive Services Task Force, 2018 (2).
Among people with non-cancerous tumors, there was a statistically significant increase in the odds of cancer.
Other reviews conflict on whether folic acid increases cancer. A review by Wien et al finds a statistically significant association with cancer. Another review by Vollset et al shows no increase in cancer.
Source: US Preventive Services Task Force, 2018 (2). Wien, 2012 (5). Vollset, 2013 (6).
Potential risk of cancer increase from over-supplementation of folic acid. Cancer is also associated with low levels of folate (4). See discussion under cancer Impact.
Source: US Preventive Services Task Force, 2018 (2). Field, 2018 (4). Wien, 2012 (5). Vollset, 2013 (6).
Vitamin C was popular for many years for immunity, but its claims have been disputed over the last few decades. This is because vitamin C was shown over many studies to have no impact on whether you would get sick with respiratory illnesses such as the common cold.2 However, positive evidence does exist for other immunity benefits, and many people, especially smokers, do not get enough vitamin C in their diet.
For background, vitamin C is an essential vitamin involved in immune system function and in the biosynthesis and metabolism of various molecules. It is also an antioxidant. The human body cannot synthesize vitamin C, so it must be ingested in your diet. Without it, scurvy develops, which involves weakness, gum disease, and bleeding.
To evaluate the impact on immunity, a systematic review of 31 trials evaluated frequency, duration, and severity of common cold symptoms. While there was no impact on whether you get sick, duration of cold symptoms decreased by 8%, and severity decreased statistically significantly as well.2 This suggests that the literature supports small immunity benefits for vitamin C overall.
Furthermore, many people lack vitamin C in their diets. 93% of female smokers and 88% of male smokers don't get enough vitamin C.1 Among non-smokers, 49% and 40% of male and female nonsmokers had vitamin C intake levels below the recommended amount. If you are a smoker or do not get enough vitamin C through your diet (i.e., through fruits and vegetables), then we recommend supplementation.
A systematic review of 29 trials found no impact on the frequency of common cold events when patients supplemented with vitamin c compared to no supplementation (2). However, duration of common cold symptoms decreased by 8%, and severity of symptoms decreased as well (2).
Source: Hemila et al, 2013
Source: US Preventive Services Task Force, 2018 (11).
Source: US Preventive Services Task Force, 2018 (11).
Source: US Preventive Services Task Force, 2018 (11).
The B-complex vitamins are popular to take for energy, improved cognitive function, or to counter a deficiency. To evaluate whether vitamin B supplementation is actually needed, we reviewed the literature for impacts on cognitive function and energy. We combined this review with deficiency rates and our knowledge of deficiency symptoms. In general, we reserve B-complex supplementation for those that can't get enough in their diet, such as vegans who can't access B12 in animal-based foods.
For background, the B vitamins are essential vitamins required for proper metabolic function. Without B1 and B3, the body cannot produce the energy it needs. Without B6, hundreds of metabolic reactions are hampered, especially those related to protein metabolism. Without B12, the central nervous system, red blood cells, and DNA synthesis cannot function properly. Deficiencies in these vitamins lead to weight loss, neurologic breakdown, weakened immunity, skin irritation, and full-blown deficiency diseases like beriberi and pellagra.
Clearly full-blown deficiencies are bad, but most people get enough of these vitamins in their diets, as shown below (note that full-blown deficiencies are rarer). Usually, deficiencies in America are not caused by suboptimal intake, but rather caused by an inability to absorb these vitamins. Vitamin B12 is an exception, since it is only available in animal-based products, which vegetarians and vegans often don't get enough of.
So what does the evidence say about supplementation?
In conclusion, the evidence for B-complex supplementation benefits is insufficient to support claims for cognitive function, energy, mood, mortality, cancer, or cardiovascular benefits. However, if a deficiency or dietary restriction is suspected, then B-complex supplementation makes sense to avoid symptoms of full-blown deficiencies.
A systematic review of the literature found only one older study on the energy impacts of b complex supplementation, which focused on blood serum indicators of energy and was not enough to draw conclusions off of (2).
Source: Markun, 2021 (2).
In a systematic review of 16 trials evaluating cognitive impacts of B complex and vitamin B12 in individuals without neurologic issues, no statistically significant impact on cognitive function was found (1). Another systematic review focused on older individuals with dementia symptoms and low B12 levels. This review found 3 trials that met the criteria, but B12 supplementation did not have a statistically significant impact on cognitive function. Overall, there is insufficient evidence to suggest that B complex or B12 provides cognitive benefits, except when serious deficiency levels are reached.
Source: Markun, 2021 (1). Malouf, 2003 (2).
One systematic review found that b-complex improved mood in a majority of studies included, but this study was funded by the nutritional supplements industry and did not have good selection criteria. In fact, they most of the studies included had interventions that also included vitamin D and other supplements along with the b-complex vitamins. (5). As a result of the bias, evidence is insufficient to say whether mood is improved.
Source: Young, 2019 (5).
No studies met the quality requirements for determining the impact of vitamin b6 impact on cancer.
Source: US Preventive Services Task Force, 2018 (4).
No studies met the quality requirements for determining the impact of vitamin b6 impact on cardiovascular disease.
Source: US Preventive Services Task Force, 2018 (4).
Vitamin B12 is commonly taken to improve cognitive function or to supplement dietary deficiencies. To evaluate whether vitamin B12 supplementation is actually needed, we reviewed the literature for impacts on cognitive function. We combine this review with deficiency rates and our knowledge of deficiency symptoms. In general, we reserve vitamin B12 supplementation for those that can't get it in their diet.
For background, vitamin B12 is an essential vitamin involved in the healthy function of the central nervous system, DNA, and red blood cells. It is primarily found in meat and foods of animal origin such as eggs and milk. Because vitamin B12 is found primarily in animal-based sources, vegans and some vegetarians have an higher risk of being deficient in this vitamin. Seeking vitamin B12 sources is important, as Vitamin B12 deficiency is serious and leads to neurologic issues, dementia, anemia, weakened immune system, weight loss, fatigue, and infertility.
However, for otherwise healthy individuals, a systematic review of 16 randomized trials found that supplementation with B12 has no impact on cognitive function.1 B12 supplementation in individuals with dementia and low B12 levels also showed no improvement in cognitive function in a review of 3 eligible studies.2 Overall, the evidence of B12 being a brain booster is weak.
Given the limited evidence for cognitive function improvement, we reserve B12 for the primary use of avoiding deficiencies. That is, we recommend B12 primarily for vegans who don't have access to animal by-products and for vegetarians who don't eat many animal by-products.
Vitamin B12 plays an essential role in central nervous system function. However, in a systematic review of 3 trials for people with low B12 and dementia symptoms, B12 supplementation did not have a statistically significant impact on cognitive function (2). In a more recent trial evaluating cognitive impact of vitamin B12 in individuals without neurologic issues, no impact on cognitive function was found across 16 randomized trials (1). Overall, there is insufficient evidence to suggest that B12 provides cognitive benefits, except when serious deficiency levels are reached.
Source: Markun, 2021 (1). Malouf, 2003 (2).
We evaluated the literature to determine the impact of iron supplementation on preventing iron deficiency anemia and conclude that intermittent dosing of iron supplements effectively prevents anemia in menstruating women while minimizing risk.
Iron is required for supplying oxygen to the body, and 19% of women aged 19-50 don't get enough iron.1 This can be caused by heavy menstrual bleeding (where iron is lost through blood loss) or pregnancy (when blood need increases).
When the body is fully deficient of iron, the cells in your blood responsible for oxygen transport start to deplete, which leads to iron deficiency anemia, which is a risk factor for many diseases.
A systematic review of the literature by Ana Gaxiola found 25 studies evaluating the impact of iron supplementation regimens on preventing anemia. Combining data across the studies, women who supplemented 1-3 times a week had 0.65 times the risk of anemia compared to women who did not supplement. This result was statistically significant across 10,996 women. Furthermore, there was no statistical difference between supplementing intermittently (1-3 times a week) compared with daily, and supplementing intermittently had 0.41 times the risk of getting side effects.2,3
To avoid iron deficiencies, women who have heavy menstrual bleeding or are pregnant should supplement their diet with iron 1-3 times a week.
A systematic review of the literature by Ana Gaxiola found 25 studies evaluating the impact of iron supplementation regimens on preventing anemia. Combining data across the studies, women who supplemented 1-3 times a week had 0.65 times the risk of anemia compared to women who did not supplement. This result was statistically significant across 10,996 women. Furthermore, there was no statistical difference between supplementing intermittently (1-3 times a week) compared with daily, and supplementing intermittently had 0.41 times the risk of getting side effects (2). Another review found similar results for iron supplementaiton, but due to a conflict of interest by the authors, we provide it only as a secondary source (3).
Sources: Gaxiola, 2019 (2). Low, 2016 (3).
The US Preventive Services Task Force could not find any studies on iron and mortality that met the quality requirements.
Source: US Preventive Services Task Force, 2018 (4).
The US Preventive Services Task Force could not find any studies on iron and cancer that met the quality requirements.
Source: US Preventive Services Task Force, 2018 (4).
The US Preventive Services Task Force could not find any studies on iron and cardiovascular disease that met the quality requirements.
Source: US Preventive Services Task Force, 2018 (4).
To assess the benefits of turmeric, we compared results from multiple systematic reviews that review the literature.1,2,3,4,5,6,7 Turmeric has long been used in eastern medicine, but what do the randomized controlled trials say?
For metabolic syndrome, pre-diabetes, and type II diabetes, all systematic reviews we found show improvements in blood pressure, HbA1c levels, fat levels, cholesterol, and more.1,5,6,7. Each of these systematic reviews combined data from randomized controlled trials to find statistically significant reductions across these critical metabolic indicators.
For patients with osteoarthritis, pain and function was improved in a meta-analyses across 10 randomized controlled trials.1,8
Turmeric may even help reduce cognitive decline, but more research is needed in this area.2
Note that the Rolfe article has a conflict of interest. However, none of our claims are based on the Rolfe article alone, since other reviews support the same findings.
Patients with metabolic syndrome in multiple meta-analyses had a statistically significant reduction in blood pressure across pooled data from 7+ systematic reviews. (1,5) Other health indicators were improved as well across multiple meta-analyses, including triglyceride (fat) levels, BMI, waist circumference, total cholesterol, leptin, and others. (1,5,7)
Another meta-analysis found statistically significant positive impacts on BMI, weight, leptin levels, and adiponectin levels using data spanning 21 randomized controlled trials (6).
Source: Rolfe, 2020 (1). Azhdari, 2019 (5). Akbari, 2019 (6). Chien, 2021 (7)
Curcumin statistically significantly reduced pain and helped reinstate physical function / mobility in osteoarthritis patients when compared to placebo. Data was aggregated across 10 randomized controlled trials in Paultre (8) and seven systematic reviews in Rolfe (1).
Source: Rolfe, 2020 (1); Paultre, 2021 (8).
Patients with pre-diabetes or type 2 diabetes had a statistically significant reduction in HbA1C across pooled data from 12 systematic reviews.
Source: Rolfe, 2020 (1).
3 of 5 studies in healthy, non-demented elderly found either reduced cognitive decline or improved cognitive performance over time, relative to placebo
Source: Voulgaropoulou, 2019 (2).
23 systematic reviews reported no serious adverse events; 15 reviews detailed adverse events which were all minor and included GI symptoms (nausea, diarrhea), headaches, sleepiness, hypertension, etc.
Source: Rolfe, 2020 (1).