Lead
"Is it okay to give my child probiotic drinks?" "Does my baby need a vitamin D supplement?" "Herbal remedies are gentler, right — they must be safe?" Complementary therapies are widely considered, and the interest is understandable.
But the quality of evidence varies enormously across products and claims. Some things can reasonably be called effective. Others cannot be called ineffective — the studies simply aren't there. This article works through three categories using a consistent framework: what condition, how much effect, under what conditions — based on the current state of the evidence, honestly.
A Starting Premise: "Natural" Does Not Mean "Safe"
The assumption that natural-origin products carry no side effects is not accurate. Anything administered to the body has the potential to affect it. The Paracelsian principle — that the dose determines the poison — applies to complementary therapies as much as to pharmaceuticals.
And "no evidence of effect" is not the same as "evidence of no effect." Some areas simply haven't been adequately studied. This article sorts claims into three categories: evidence of benefit, weak rationale, and requires caution.
Probiotics
Where the Evidence Is Strongest: Acute Infectious Diarrhea
The most consistent body of evidence for probiotics in children applies to shortening the duration of acute infectious diarrhea.
A 2013 meta-analysis by Szajewska et al. found that Lactobacillus rhamnosus GG (LGG: a well-studied probiotic bacterial strain with documented evidence for shortening acute infectious diarrhea in children) reduced the duration of acute diarrhea by an average of 0.9–1.1 days [1]. Saccharomyces boulardii is also supported by multiple RCTs. The 2014 ESPGHAN/ESPID guidelines list specific strains such as LGG and S. boulardii among the treatment options that can be added to oral rehydration [2]. The AAP (American Academy of Pediatrics) offered qualified support for probiotics in acute diarrhea in a 2010 statement [3].
That said, a large double-blind RCT run in 10 US pediatric emergency departments in 2018 (971 children aged 3 months to 4 years) found that a 5-day course of LGG did no better than placebo — no difference in progression to moderate-to-severe illness or in the duration of diarrhea [4]. The benefit seen in meta-analyses may be small, or vanish, depending on trial conditions. The fair framing is "an optional supportive measure," not a substitute for rehydration.
Where the Evidence Is Weak
For constipation, allergy prevention, and upper respiratory tract infections, consistency across trials is poor. The current evidence base is insufficient to support recommendations for any of those indications. The widespread framing around "improving the gut environment" sounds plausible, but it should not be conflated with demonstrated efficacy for specific symptoms from specific strains.
What to Watch For
Probiotic products vary enormously in strain identity and colony count. A label saying "contains live cultures" or "with lactobacillus" does not establish efficacy. Additionally, administering live organisms to an immunocompromised child carries a small risk of sepsis; this use is specifically not recommended [3].
Vitamin D
Where the Recommendation Is Clearest: Supplementation for Breastfed Infants
Of the three, vitamin D has the clearest recommendation: the AAP makes a specific numerical one. Japan's guidance, however, is not the same as the AAP's (see below).
Human milk is low in vitamin D (often a few tens of IU per liter) — nowhere near the 400 IU/day recommended for infants [5][6]. Since the Wagner and Greer (2008) AAP statement, the standard US recommendation has been: exclusively and partially breastfed infants (those drinking less than about 1 L of formula a day) should receive 400 IU/day of vitamin D beginning soon after birth [5].
Japan takes a somewhat different position. A 2025 proposal from the Nutrition Committee of Japan's pediatric health-care council (日本小児医療保健協議会), published in the Journal of the Japan Pediatric Society, centers on lifestyle and dietary guidance — reasonable time outdoors, avoiding excessive sunscreen, not delaying complementary foods — and says to consider an infant vitamin D supplement when that is hard to achieve (for example, in winter or at high latitudes). It states plainly that the universal supplementation to age 1 recommended by international guidelines "is not yet practiced in Japan," and lists it as an issue needing discussion [6].
Vitamin D-deficiency rickets: a bone-softening disease in children caused by insufficient vitamin D, leading to bowed legs, skeletal deformity, and impaired growth is not a historical disease. In Japan, vitamin D deficiency in infants is reported to be increasing with changes in lifestyle and diet, and one study found more than half of infants aged 0–5 months were deficient [6].
Ceiling and Overdose
The Institute of Medicine (IOM) Dietary Reference Intakes set the tolerable upper intake level for infants at 1,000 IU/day for ages 0–6 months and 1,500 IU/day for 6–12 months [7]. Many commercially available drops deliver 400 IU per drop, making dose management relatively straightforward — though products vary, so checking the concentration at purchase is essential.
"Sunlight is enough" is not a reliable assumption. The UV (UVB) that makes vitamin D depends on season, latitude, weather, and time outdoors, and it barely passes through window glass [6]. Japan's proposal recommends reasonable outdoor time and, where that falls short, considering a supplement. If you use one, follow the product's directions and check with your pediatrician [6].
Herbal Medicine (Kampo)
Commonly Used Formulas and the State of the Evidence
Traditional Japanese herbal medicine (Kampo) is widely prescribed in Japanese pediatric practice; it is covered by national health insurance and used in pediatrics too. Here is the evidence picture for three commonly used formulas.
| Formula | Primary indication | Controlled trials in children | Assessment |
|---|---|---|---|
| Yokukansan | Night crying, nervous irritability | No blinded RCTs found (mainly small open-label studies) | Limited reports of improvement |
| Shokenchuto | Constitutional weakness, recurrent abdominal pain | Sparse, as far as we could find | Mainly observational studies and clinical experience |
| Goreisan | Vomiting, headache | Sparse, as far as we could find | Used for vomiting in acute gastroenteritis, but few controlled trials |
A 12-week prospective open-label study by Wake et al. (2013; 20 children aged 6–17 with pervasive developmental disorder) reported improvement in irritability — tantrums, aggression — with yokukansan. But it was small, had no control group, and was not blinded; the authors themselves called for larger placebo-controlled trials, so the result should be read cautiously [8].
"Herbal Does Not Mean Safe"
The critical point about Kampo is that it has side effects. Formulas containing kanzō (licorice root) — including shakuyaku-kanzō-tō and shokenchuto — can cause pseudoaldosteronism: a drug-induced syndrome mimicking excess aldosterone, characterized by low potassium, high blood pressure, and fluid retention (hypokalemia: abnormally low potassium levels in the blood, which can cause muscle weakness, cramps, or cardiac arrhythmia). Risk depends on the licorice dose, so combining several licorice-containing formulas stacks the amount. It is said to occur more easily in people with a small body surface area, and it is more likely — and more severe — alongside drugs that can themselves lower potassium, such as diuretics and corticosteroids. Using these preparations on the assumption that they have no side effects is a mistake [9].
Kampo granule preparations are also designed around adult dosing — dose adjustment for children requires expertise. Kampo use in children should involve a physician or pharmacist with pediatric prescribing experience.
Putting It Into Practice
1. Using LGG or S. boulardii as a supportive measure during acute diarrhea is one evidence-supported option. The effect is modest at best and does not replace fluids. Verify the strain name on the label — "contains probiotics" does not identify the strain.
2. For a breastfed infant, talk to your pediatrician about vitamin D supplementation alongside outdoor time and complementary foods. The AAP recommends 400 IU/day from soon after birth; Japan's proposal says to consider a supplement when lifestyle can't cover it. If you use drops, check the amount per drop and follow the directions.
3. If considering Kampo, do not start from the assumption that it carries no side effects. Consult a physician or pharmacist with pediatric Kampo experience; ask about side effects and interactions with any other medications the child is taking.
Summary
The effectiveness categories are real distinctions. Probiotics for acute diarrhea are supported by multiple meta-analyses (though a large RCT found no benefit); probiotics for constipation or allergy prevention are not, at least not yet. Vitamin D supplementation for breastfed infants is recommended by the AAP and international consensus (Japan's guidance is conditional), and there is an upper limit to respect. Kampo is widely prescribed but not free of adverse effects.
When evaluating any complementary therapy, the productive question is not "is it natural?" but "what is the evidence for this specific claim, in this condition, at this dose?"
References
- Szajewska H, Skórka A, Ruszczyński M, Gieruszczak-Białek D. Meta-analysis: Lactobacillus GG for treating acute gastroenteritis in children — updated analysis of randomised controlled trials. Aliment Pharmacol Ther. 2013;38(5):467–476. PMID: 23841880.
- Guarino A, Ashkenazi S, Gendrel D, et al. European Society for Pediatric Gastroenterology, Hepatology, and Nutrition/European Society for Pediatric Infectious Diseases evidence-based guidelines for the management of acute gastroenteritis in children in Europe: update 2014. J Pediatr Gastroenterol Nutr. 2014;59(1):132–152. PMID: 24739189.
- Thomas DW, Greer FR; American Academy of Pediatrics Committee on Nutrition; Section on Gastroenterology, Hepatology, and Nutrition. Probiotics and prebiotics in pediatrics. Pediatrics. 2010;126(6):1217–1231. PMID: 21115585.
- Schnadower D, Tarr PI, Casper TC, et al. Lactobacillus rhamnosus GG versus placebo for acute gastroenteritis in children. N Engl J Med. 2018;379(21):2002–2014. PMID: 30462938.
- Wagner CL, Greer FR; American Academy of Pediatrics Section on Breastfeeding; Committee on Nutrition. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008;122(5):1142–1152. PMID: 18977996.
- Nutrition Committee, Japanese pediatric health-care council (日本小児医療保健協議会栄養委員会). Proposal on the prevention of vitamin D deficiency in infancy (乳児期のビタミンD欠乏の予防に関する提言). J Jpn Pediatr Soc. 2025;129(3):494–496. [in Japanese]
- Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press; 2011. PMID: 21796828.
- Wake R, Miyaoka T, Inagaki T, et al. Yokukansan (TJ-54) for irritability associated with pervasive developmental disorder in children and adolescents: a 12-week prospective, open-label study. J Child Adolesc Psychopharmacol. 2013;23(5):329–336. PMID: 23782127.
- Ministry of Health, Labour and Welfare (Japan). Manual for handling serious adverse drug reactions: pseudoaldosteronism (重篤副作用疾患別対応マニュアル 偽アルドステロン症). 2006; revised February 2022. [in Japanese]