NOW Vitamin D3 1000 IU review: does vitamin D help testosterone?

Vitamin D is one of the most common deficiencies in the world, including in sunny countries where people spend most of the day indoors and cover up outside. Because vitamin D receptors are found in the testes, it has become a popular supplement for men interested in testosterone. This review looks at what the research shows and whether this NOW Foods softgel is a sensible way to take it.

What is in this product

According to the Amazon listing, each softgel contains 25 mcg (1,000 IU) of vitamin D3 as cholecalciferol, sourced from lanolin (sheep's wool), in extra virgin olive oil. The capsule is made from bovine gelatin, glycerin and water. The bottle contains 360 softgels.

D3 is the form most studies use, and taking it in oil, or with a meal containing fat, helps absorption. The capsule uses bovine gelatin and the listing does not say it is halal certified, so check the bottle if that matters to you.

What the studies found

Pilz and colleagues (2011) randomised 54 overweight men taking part in a weight-loss programme to vitamin D or placebo for a year. Most started with low vitamin D. Total, free and bioactive testosterone rose in the vitamin D group but not in the placebo group.

Lerchbaum and colleagues (2019) ran a larger and stricter trial: 100 men who already had low testosterone but healthy vitamin D levels took vitamin D or placebo for twelve weeks. There was no meaningful change in testosterone.

Hosseini Marnani and colleagues (2019) pooled the clinical trials in a meta-analysis and found no significant overall effect of vitamin D on total testosterone in men.

How to read these results

Put together, the evidence suggests vitamin D is unlikely to raise testosterone in men whose levels are already normal. The positive result came mainly in men who started out low in vitamin D. Correcting a deficiency is worthwhile for bones, muscles and general health in its own right, and any testosterone benefit should be seen as a possible bonus, not a promise.

The most useful step is a simple blood test (25-hydroxyvitamin D) so you know whether you are actually low, rather than guessing.

Safety

At the amount in this softgel, vitamin D is generally well tolerated. The NIH sets the upper limit for adults at 4,000 IU (100 mcg) a day from all sources. Taking far more than you need for long periods can raise calcium levels and cause problems such as nausea, weakness and kidney stones. Vitamin D can interact with some medicines, including certain diuretics, steroids and weight-loss drugs. Talk to a doctor or pharmacist before starting, especially if you have kidney disease, high calcium or take regular medication.

Verdict

This is a plain, reliable vitamin D3 product from a long-established brand, with a modest amount per softgel and a large bottle. If a blood test shows you are low, it is a sensible, inexpensive option to discuss with your doctor. If your levels are normal, it is unlikely to do much for testosterone.

This review summarises published research and the manufacturer's listing. It is not medical advice.