N-acetyl glucosamine: the trials are sound, both are from the maker, and the big one is a combination

A 2010 trial in Br J Dermatol. Ten weeks, double-blind, vehicle-controlled, full-face, parallel-group.

It was conducted in women aged 40 to 60, and after a two-week washout they used one of two daily regimens.

• test formulation, 101 people — a morning SPF 15 sunscreen lotion and an evening cream, both containing 4% niacinamide + 2% NAG
• vehicle control, 101 people — the vehicles of the same lotion and cream

The assessment is this entry's strength. Digital photographs at 0, 4, 6 and 8 weeks were evaluated in four ways.

• algorithm-based computer image analysis for coloured spot area fraction
• expert visual grading
• non-contact SIAscopy for melanin spot area fraction
• and, the same way, melanin chromophore evenness

Result: by all four measures the NAG + niacinamide regimen was significantly (P < 0.05) more effective than the vehicle control in reducing the detectable area of facial spots and the appearance of pigmentation.

Now how to read it.

First, 202 people. A rare size among the ingredient pages here. And it is double-blind and vehicle-controlled.

Second, it was measured by instrument. Not only visual grading but computer image analysis and SIAscopy values. So the endpoint is marked 'instrument'. On the distinction this site keeps returning to — measuring versus looking — this is the measuring side.

Third, but it is a combination. That is this entry's largest limit. 4% niacinamide is in there too. And the paper itself introduces niacinamide as 'an agent previously shown to be clinically active'. Which is to say, a formulation with NAG added on top of something already known to work was compared against vehicle.

So what the trial shows is 'this combination beats vehicle', not 'NAG does this much'. This site drew the same distinction on the pycnogenol page.

Fourth, the morning product contained SPF 15. It was in both arms, so it is not what made the difference. But remember that in pigmentation, sunscreen is not background but a condition.

Fifth, the funding. Procter & Gamble appears among the authors' affiliations. This site marks that as industry funding. And 'strong evidence' here is not attached when all the trials are industry-funded. Since both are, this ingredient's badge stops in the middle structurally.

Sixth, eight weeks of use in a ten-week trial. Nothing past that was looked at.

So it sits at 'moderate'. The size, the design and the instrument measurement are good; being a combination and the funding set the ceiling.

A 2007 trial in J Cosmet Dermatol. This entry partly covers the problem that the one above looked only at a combination.

The paper reports three things.

First, cell culture data. Glucosamine has been reported to inhibit melanin production, which is the starting point for a possible topical use. This site does not count cell culture as a result in people.

Second, skin penetration. Franz cell testing found NAG to be a good skin penetrant. That is in-vitro material.

Third, the trial in people. This is the body of the entry.

• 8 weeks, double-blind, placebo-controlled, left-right randomised, split-face
• topical 2% NAG reduced the appearance of facial hyperpigmentation

And in a second study it reports that adding 4% niacinamide to 2% NAG gave a greater effect on hyperpigmentation. The entry above is the large trial in that direction.

Now how to read it.

First, the design is good. Left-right randomised split-face compares within one person, so age, skin and daily life cancel out. It is double-blind and placebo-controlled.

Second, but the abstract gives no participant count. How many took part is not there. We do not invent it. That is why the participant field on the badge above is empty. And without the number, the weight of the result cannot be read.

Third, what the endpoint was is also unclear in the abstract. It says only that it 'reduced the appearance of hyperpigmentation'. Whether that was measured by instrument or graded by eye is not stated, so this site marks it conservatively as 'graded'.

Fourth, the funding. The authors' affiliation is Procter & Gamble. The paper concludes that NAG is 'a suitable cosmetic ingredient'. That sentence says what the paper was written for. This site does not hide that; it puts it on the badge.

Fifth, eight weeks.

So it sits at 'early evidence'. The design is good but there is no participant count, the endpoint is unclear, and the funding is industry.

Put the two entries side by side and you can see the shape of this ingredient's evidence. The solo trial has no participant count, the trial with a clear count is a combination, and both come from the same maker. That is why this site stops the badge in the middle.